Resin composition for resin-coated sand, and resin-coated sand

Abstract

This resin composition for a resin-coated sand is characterized by containing: at least one of a lignin-modified phenol resin and a mixture of lignin and a phenol resin, and a nitrate (potassium nitrate, sodium nitrate, magnesium nitrate, etc.) or a phosphoric acid ester. The composition can further contain a curing agent, a lubricant, a silane coupling agent, and so forth.

Description

Resin composition for resin-coated sand and resin-coated sand

[0001] The present invention relates to resin-coated sand and a phenolic resin composition for use in producing the resin-coated sand.

[0002] Conventionally, shell molding has been used to precisely manufacture cores, which are used as molds for casting. This shell molding method is a technique for producing hardened molded bodies for use as molds by filling a mold with granular resin-coated sand, which is made by coating the surface of aggregate with a binder containing a resin component, and firing the resulting sand. Phenolic resins are widely used as the resin component of the binder (see, for example, Patent Document 1).

[0003] After using resin-coated sand to produce hardened molded bodies, such as foundry molds and cores, the cores are placed in predetermined positions within the foundry mold. Molten metal is then poured between the foundry mold and core, and the resulting mixture is cooled to form the desired casting (cast product). To recover the casting, the foundry molds and cores are then disintegrated by vibration using a vibrator such as a knockout machine. If this disintegration process were easy, the castings could be recovered more easily and economically. Therefore, a method has been proposed in which a disintegrant is incorporated into the resin-coated sand used to form the foundry molds and cores.

[0004] For example, Patent Document 2 discloses a foundry sand binder containing a phenolic thermosetting resin, 0.1 to 20 wt % of a phthalyl polymerizable substance, 0.002 to 1.4 wt % of a radical polymerization accelerator that begins to function at 140 to 160°C, and 1 to 10 wt % of a bromine-containing organic compound that generates bromine gas upon heating, and describes that the bromine-containing organic compound is preferably an aryl bromide such as tetrabromobisphenol A. Patent Document 3 discloses a shell mold resin composition containing, per 100 wt % of a phenol / formaldehyde resin used to produce easily collapsible molds for aluminum and light alloy castings, 1 to 30 wt % of a disintegrant selected from amino acids or alkali metal salts, alkaline earth metal salts, hydrochlorides, and sulfates of amino acids, as well as alkyl esters and hydrochlorides of said alkyl esters.

[0005] International Publication 2023 / 223996 JP 8-10897 Publication JP 10-193033 Publication

[0006] An object of the present invention is to provide resin-coated sand that is suitable as a raw material for producing casting molds and that provides casting molds that have excellent disintegrability after production of a casting, and a resin composition for resin-coated sand that is used in producing the same.

[0007] The present inventors have found that the above-mentioned problems can be solved by subjecting resin-coated sand obtained using a resin composition for resin-coated sand, which is a combination of at least one of a lignin-modified phenolic resin and a mixture of lignin and a phenolic resin, and a nitrate, to molding.

[0008] The present invention is described below. [1] A resin composition for use in the production of resin-coated sand, comprising at least one of a lignin-modified phenolic resin and a mixture of lignin and a phenolic resin, and a nitrate. [2] A resin composition for use in the production of resin-coated sand, comprising at least one of a lignin-modified phenolic resin and a mixture of lignin and a phenolic resin, and a phosphate ester. [3] The resin composition for use in resin-coated sand according to [1] or [2] above, wherein the lignin-modified phenolic resin is a reaction product of at least one lignin selected from kraft lignin, soda lignin, and acetate lignin, with a phenol and an aldehyde. [4] The resin composition for use in resin-coated sand according to any one of [1] to [3] above, further comprising a curing agent. [5] The resin composition for use in resin-coated sand according to any one of [1] to [4] above, further comprising a lubricant. [6] The resin composition for resin-coated sand according to any one of [1] to [5] above, further containing a silane coupling agent. [7] The resin composition for resin-coated sand according to [1], [3], [4], [5], or [6] above, wherein the nitrate is an alkali metal salt or an alkaline earth metal salt. [8] The resin composition for resin-coated sand according to [7] above, wherein the nitrate is potassium nitrate. [9] The resin composition for resin-coated sand according to any one of [2] to [6] above, wherein the phosphate ester is an aliphatic phosphate ester.

[10] Resin-coated sand comprising at least one of a lignin-modified phenolic resin and a mixture of lignin and a phenolic resin, a nitrate, and an aggregate.

[11] The resin-coated sand according to

[10] above, wherein at least a portion of the surface of the aggregate is coated with a composition comprising at least one of the lignin-modified phenolic resin and the mixture of lignin and a phenolic resin, and the nitrate.

[12] Resin-coated sand comprising at least one of a lignin-modified phenolic resin and a mixture of lignin and a phenolic resin, a phosphate ester, and an aggregate.

[13] The resin-coated sand according to

[12] , wherein at least a portion of the surface of the aggregate is coated with a composition comprising at least one of the lignin-modified phenolic resin and the mixture of lignin and a phenolic resin, and the phosphate ester.

[14] The resin-coated sand according to

[12] or

[13] , wherein the phosphate ester is an aliphatic phosphate ester.

[0009] By using the resin composition for resin-coated sand of the present invention together with aggregate, resin-coated sand suitable for producing casting molds and the like can be obtained. Furthermore, when the resin-coated sand of the present invention is subjected to, for example, a shell molding method to produce a casting, the resulting mold exhibits excellent disintegration properties. Therefore, parts containing metals or alloys used in various industries can be efficiently produced.

[0010] The present invention will be described below. The matters set forth herein are for illustrative purposes and are intended to exemplify embodiments of the present invention, and are set forth in order to provide what is believed to be the most effective and easily understandable explanation of the principles and conceptual features of the present invention. In this respect, it is not intended to show structural details of the present invention beyond the extent necessary for a fundamental understanding of the present invention, but rather to clarify to those skilled in the art how some aspects of the present invention can be actually embodied.

[0011] The resin composition for resin-coated sand of the present invention is a raw material for producing resin-coated sand, which is used to obtain shaped articles such as casting molds composed of cured molded bodies by filling a mold and firing it. The resin composition for resin-coated sand of the present invention is characterized by containing at least one of a lignin-modified phenolic resin and a mixture of lignin and a phenolic resin (a phenolic resin not modified with lignin), as well as a nitrate or a phosphate ester. The resin composition for resin-coated sand of the present invention can further contain other components (described below) as necessary.

[0012] The lignin-modified phenolic resin according to the present invention may be either a lignin-modified novolac phenolic resin or a lignin-modified resol phenolic resin, or both. In the present invention, from the viewpoint of the storage stability of the resin-coated sand, it is preferable that the resin-coated sand contains a lignin-modified novolac phenolic resin.

[0013] Lignin-modified phenolic resins are reaction products of lignin, phenols, and aldehydes.

[0014] Lignin is a polymeric phenolic compound consisting of a basic skeleton such as guaiacyl lignin (G type), syringyl lignin (S type), and p-hydroxyphenyl lignin (H type), and is found in all plants.

[0015] Lignin is classified, for example, by the production method. Specific examples include explosion lignin obtained by treating plants by explosion method, and digested lignin (kraft lignin) obtained by treating plants by cooking method.

[0016] Lignin is also classified according to the type of plant from which it is derived, and examples include lignin derived from woody plants and lignin derived from herbaceous plants.

[0017] Examples of woody plant-derived lignins include coniferous lignins contained in conifers such as cedar, hardwood lignins contained in hardwoods, etc. Such woody plant-derived lignins do not contain lignins having an H-type skeleton, whereas coniferous lignins have a G-type skeleton and hardwood lignins have both G-type and S-type skeletons.

[0018] Examples of lignins derived from herbaceous plants include rice lignins contained in grasses (wheat straw, rice straw, corn, bamboo, etc.) Such herbaceous plant-derived lignins have all of the H-, G-, and S-type skeletons.

[0019] The lignin is preferably lignin derived from a herbaceous plant, and more preferably lignin derived from a herbaceous plant derived from corn stover (corn cobs, stalks, leaves, etc.).

[0020] Furthermore, from the viewpoint of reactivity with phenols and the like, the lignin preferably contains 3% by mass or more of an H-type basic skeleton, more preferably 9% by mass or more, and even more preferably 14% by mass or more.

[0021] Such lignin can be extracted as alkaline lignin from pulp waste liquor (black liquor) obtained by cooking plant materials (coniferous trees, broad-leaved trees, grasses, etc.) that serve as the raw material for lignin with an alkaline agent such as caustic soda.

[0022] Lignin may also be modified with an acid, which may be an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, or an organic acid such as a carboxylic acid (acetic acid, propionic acid, butyric acid, lauric acid, or the like) or a sulfonic acid.

[0023] In the present invention, kraft lignin, soda lignin, acetic acid lignin, etc. are preferably used as the lignin.

[0024] Phenols refer to phenol and its derivatives (phenol-modified compounds), and examples of the latter derivatives include alkylphenols such as o-cresol, p-cresol, p-tert-butylphenol, p-phenylphenol, p-cumylphenol, p-nonylphenol, 2,4- or 2,6-xylenol, m-cresol, resorcinol, and 3,5-xylenol, polyhydric phenols such as bisphenol A and dihydroxydiphenylmethane, and naphthol. Furthermore, halogenated phenols obtained by substituting hydrogen atoms in these compounds with halogen atoms such as chlorine atoms and bromine atoms can also be used as derivatives. Of these, phenol is preferred.

[0025] Examples of aldehydes include formaldehyde, paraformaldehyde, acetaldehyde, propionaldehyde, butylaldehyde (n-butylaldehyde, isobutylaldehyde), furfural, glyoxal, benzaldehyde, trioxane, tetraoxane, etc. Of these, formaldehyde and paraformaldehyde are preferred.

[0026] When aldehydes are reacted with lignin and phenols, an aqueous solution of the aldehydes can be used.

[0027] Lignin-modified novolac phenolic resins can be synthesized by reacting lignin, phenols, and aldehydes under heating in the presence of an acid catalyst. In this case, the preferred amounts of each raw material are as follows: The amount of phenols used is preferably 100 to 900 parts by mass, more preferably 150 to 900 parts by mass, based on 100 parts by mass of lignin. The amount of aldehydes used is preferably 10 to 400 parts by mass, more preferably 10 to 350 parts by mass, based on 100 parts by mass of lignin.

[0028] Examples of the acid catalyst include organic acids, inorganic acids, and acidic substances. Examples of organic acids include sulfonic acid compounds such as methanesulfonic acid, p-toluenesulfonic acid, dodecylbenzenesulfonic acid, cumenesulfonic acid, dinonylnaphthalene monosulfonic acid, dinonylnaphthalenedisulfonic acid, benzenesulfonic acid, and xylenesulfonic acid; phosphate esters having an alkyl group having 1 to 18 carbon atoms such as trimethyl phosphate, triethyl phosphate, monobutyl phosphate, dibutyl phosphate, tributyl phosphate, and trioctyl phosphate; and formic acid, acetic acid, and oxalic acid. Examples of inorganic acids include phosphoric acid, hydrochloric acid, sulfuric acid, and nitric acid. Examples of acidic substances include zinc oxide, zinc chloride, magnesium oxide, and zinc acetate.

[0029] The amount of the acid catalyst used is preferably 0.1 to 3.0 parts by mass, more preferably 0.2 to 2.0 parts by mass, based on 100 parts by mass of the amount of the phenol used.

[0030] Lignin-modified resole-type phenolic resins can be synthesized by reacting lignin, phenols, and aldehydes under heating in the presence of a basic catalyst or a divalent metal catalyst. Examples of basic catalysts include alkali metal or alkaline earth metal hydroxides such as sodium hydroxide and calcium hydroxide, alkaline earth metal oxides, amines such as dimethylamine, triethylamine, butylamine, dimethylbenzylamine, and naphthalenediamine, ammonia, and hexamethylenetetramine. Examples of divalent metal catalysts include divalent metal naphthenates and divalent metal hydroxides. The molar ratio (F / P) of aldehydes to phenols in such condensation reactions is appropriately selected depending on the type of reaction catalyst used, but is generally selected within the range of 1.1 to 4.0.

[0031] The novolac type phenolic resins and resol type phenolic resins may be used alone or in combination in an appropriate ratio without any problem. As is well known, modified phenolic resins obtained by replacing part of the phenol with components such as bisphenol A and naphthol may also be used. Furthermore, they may also be used as benzylic ether type phenolic resins.

[0032] When reacting lignin, phenols, and aldehydes, a method of supplying all of these components to the reaction system and reacting them, or a method of sequentially supplying specific components to the reaction system and reacting them, can be applied. A specific example of the latter method is a method of first reacting lignin with phenols and then reacting the resulting reaction product with aldehydes.

[0033] The lignin modification rate in the lignin-modified phenolic resin according to the present invention is preferably 10 to 50%, more preferably 10 to 40%, from the viewpoints of environmental considerations and mold properties. The lignin modification rate is calculated using the following formula: Lignin modification rate (%) = [(amount of lignin used) / (amount of lignin used + amount of phenols used)] x 100

[0034] The average molecular weight of the lignin-modified phenolic resin according to the present invention is not particularly limited, but from the viewpoint of mold properties, the number average molecular weight in terms of polystyrene measured by GPC is preferably 200 to 2,000, more preferably 300 to 1,500.

[0035] The resin composition for resin-coated sand of the present invention may contain one or more types of lignin-modified phenolic resins.

[0036] In the present invention, a mixture of lignin and a phenolic resin (a phenolic resin not modified with lignin, hereinafter simply referred to as "phenolic resin") can be used instead of the lignin-modified phenolic resin. The lignin can contain only one or two or more of the above-mentioned lignins that can be used to produce the lignin-modified phenolic resin. The lignin is preferably acetic acid lignin or soda lignin. Furthermore, the phenolic resin can be a conventionally known novolac-type phenolic resin, a resol-type phenolic resin, or the like, and of these, a novolac-type phenolic resin is preferred.

[0037] The average molecular weight of the phenolic resin is not particularly limited, but from the viewpoint of mold properties, the number average molecular weight as converted into polystyrene by GPC is preferably 200 to 2,000, more preferably 300 to 1,500.

[0038] In the present invention, the contents of lignin and phenolic resin are preferably 10 to 50% by mass and 50 to 90% by mass, more preferably 10 to 40% by mass and 60 to 90% by mass, respectively, when the total of both is 100% by mass.

[0039] The nitrate and phosphate ester according to the present invention are components (disintegrants) that improve the disintegration properties of molds and the like after casting production. Nitrate is a nitrate ion (NO ３ －In the present invention, one or more nitrates selected from sodium nitrate, potassium nitrate, ammonium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate, manganese nitrate, cobalt nitrate, copper nitrate, zinc nitrate, iron nitrate, etc. can be used. Of these, potassium nitrate is preferred.

[0040] The phosphate ester is not particularly limited as long as it has a structure of an ester reaction product between an organic compound having a hydroxy group and phosphoric acid. In the present invention, one or more compounds selected from aliphatic compounds, alicyclic compounds, and aromatic compounds can be used. The phosphate ester may be either a condensed or non-condensed type.

[0041] Representative structures of phosphate esters are shown in the following general formulas (1) and (2).

[0042] (In the formula, R １ , R ２ and R ３ are the same or different hydrocarbon groups.

[0043] (In the formula, R ４ , R ５ , R ７ and R ８ are the same or different hydrocarbon groups, and R ６ is a divalent hydrocarbon group, and n is a number of 1 or more.

[0044] In the above general formulas (1) and (2), R １ , R ２ , R ３ , R ４ , R ５ , R ７ and R ８ can be a monovalent hydrocarbon group such as a linear or branched saturated hydrocarbon group, a linear or branched unsaturated hydrocarbon group, or a hydrocarbon group containing an aromatic ring.

[0045] In the above general formula (2), R ８can be a divalent hydrocarbon group such as a linear or branched saturated hydrocarbon group or a hydrocarbon group containing an aromatic ring. In the general formula (2), n is preferably 1 to 10.

[0046] The phosphate ester according to the present invention preferably contains a condensed compound, and particularly preferably contains an aliphatic compound (aliphatic phosphate ester).

[0047] In the present invention, the content of nitrate contained in the resin composition for resin-coated sand used in the production of resin-coated sand that provides a mold or the like that exhibits excellent disintegration properties after the production of a casting is preferably 5 to 20 parts by mass, and more preferably 5 to 15 parts by mass, relative to 100 parts by mass of the content of at least one of the lignin-modified phenolic resin and the mixture of lignin and phenolic resin (phenolic resin not modified with lignin).

[0048] In the present invention, the content of the phosphate ester contained in the resin composition for resin-coated sand used in the production of resin-coated sand that provides a mold or the like that exhibits excellent disintegration properties after the production of a casting is preferably 5 to 20 parts by mass, and more preferably 5 to 15 parts by mass, relative to 100 parts by mass of the content of at least one of the lignin-modified phenolic resin and the mixture of lignin and phenolic resin (phenolic resin not modified with lignin).

[0049] When producing resin-coated sand, it is preferable to use a resin composition for resin-coated sand whose nitrate or phosphate ester content falls within the above-mentioned range. However, just before producing the resin-coated sand, a resin composition for resin-coated sand whose nitrate or phosphate ester content falls within the above-mentioned range may be prepared by mixing a resin composition for resin-coated sand containing at least one of a lignin-modified phenolic resin and a mixture of lignin and phenolic resin (phenolic resin not modified with lignin), and a nitrate or phosphate ester, and whose nitrate or phosphate ester content falls below the lower limit of the above-mentioned preferred range, with a separately prepared nitrate or phosphate ester.

[0050] As described above, the resin composition for resin-coated sand of the present invention can contain other components, such as a curing agent (curing accelerator), a lubricant, a coupling agent, a plasticizer, a release agent, a flame retardant, a stabilizer, and a colorant. These components may be added during the production of the lignin-modified phenolic resin or phenolic resin used as a resin binder, or during the production of the resin-coated sand.

[0051] As the curing agent, conventionally known compounds can be used as curing agents for phenolic resins. In the present invention, tertiary amines are preferred, and hexamethylenetetramine is particularly preferred. Curing can also be achieved by using a novolac-type phenolic resin and a resol-type phenolic resin in combination. Examples of additives that have the effect of accelerating the curing reaction include organic phosphines, imidazoles, cycloamidine compounds, quinone compounds, slaked lime, benzoic acid, salicylic acid, para-aminobenzoic acid, anthranilic acid, aromatic carboxylic acids such as phthalic acid and terephthalic acid, and diamines such as ethylenediamine and triethylenediamine. These can be used alone or in combination of two or more.

[0052] When the resin composition for resin-coated sand of the present invention contains a curing agent, the content ratio of the curing agent is preferably 1 to 30 parts by mass, more preferably 5 to 25 parts by mass, relative to 100 parts by mass of the content of the lignin-modified phenolic resin or the total content of the mixture of lignin and phenolic resin.

[0053] Lubricants are used to improve the fluidity of resin-coated sand or to improve the releasability of a cured molded article produced from the resin-coated sand using a mold. Examples of lubricants suitable for this purpose include waxes such as paraffin wax, synthetic polyethylene wax, carnauba wax, and montanic acid wax; fatty acid amides such as stearic acid amide, oleic acid amide, and erucic acid amide; alkylene fatty acid amides such as methylene bis-stearic acid amide and ethylene bis-stearic acid amide; stearic acid, stearyl alcohol, metal stearates (e.g., lead stearate, zinc stearate, calcium stearate, and magnesium stearate), stearic acid monoglyceride, and stearyl stearate. These may be used alone or in combination of two or more.

[0054] When the resin composition for resin-coated sand of the present invention contains a lubricant, the content thereof is preferably 0.2 to 15 parts by mass, more preferably 0.3 to 10 parts by mass, relative to 100 parts by mass of the content of the lignin-modified phenolic resin or the total content of the mixture of lignin and phenolic resin.

[0055] Coupling agents are used to improve the binding ability of the resin composition for resin-coated sand to aggregate or to improve the strength of the cured molded product. Suitable coupling agents for imparting such effects include silane coupling agents, zirconium coupling agents, and titanium coupling agents, with silane coupling agents being particularly preferred. Examples of silane coupling agents include silane coupling agents having an amino group, such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-methyl-3-aminopropyltrimethoxysilane, N-ethyl-3-aminopropyltrimethoxysilane, N-butyl-3-aminopropyltrimethoxysilane, N,N-dimethyl-3-aminopropyltrimethoxysilane, N,N-diethyl-3-aminopropyltrimethoxysilane, and N,N-dibutyl-3-aminopropyltrimethoxysilane. Of these, 3-aminopropyltriethoxysilane is preferred.

[0056] When the resin composition for resin-coated sand of the present invention contains a coupling agent, the content thereof is preferably 0.05 to 5 parts by mass, more preferably 0.1 to 3 parts by mass, relative to 100 parts by mass of the content of the lignin-modified phenolic resin or the total content of the mixture of lignin and phenolic resin.

[0057] Examples of the release agent include fluorine-based release agents, silicone-based release agents, etc. Other additives that can be used include light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, graphite fine particles, mica, vermiculite, iron sand, red iron oxide, and deodorants.

[0058] The resin-coated sand of the present invention is a granular product comprising the resin composition for resin-coated sand of the present invention and aggregate. The resin-coated sand of the present invention is usually a composite in which at least a portion of the surface of the aggregate is coated with the resin composition for resin-coated sand, and is a granular product comprising an aggregate part made of aggregate and a coating part formed on the surface of the aggregate part. The resin-coated sand of the present invention is preferably a granular product comprising a coating part formed on the entire surface of the aggregate part.

[0059] Since the hardened molded article obtained using the resin-coated sand of the present invention is usually used as a mold, inorganic particles having fire resistance sufficient to withstand casting are preferably used as the aggregate constituting the resin-coated sand. Examples of inorganic particles that can be used include natural aggregates containing quartz as the main component, such as silica sand, flattery sand, alumina sand, chromite sand, zircon sand, olivine sand, and mullite sand; and synthetic aggregates, such as synthetic mullite sand, magnesia, and fly ash.

[0060] The shape and size of the aggregate (aggregate portion) are not particularly limited. The size is preferably 20 to 100 in terms of AFS index.

[0061] The coating portion constituting the resin-coated sand of the present invention contains a resin composition for resin-coated sand, and therefore contains at least one of a lignin-modified phenolic resin and a mixture of lignin and a phenolic resin, and a nitrate or a phosphate ester. As described above, the resin composition for resin-coated sand can contain other components such as a curing agent and a lubricant, and therefore the coating portion can also contain other components as they are.

[0062] From the viewpoint of formability of a hardened molded body, the mass ratio of the aggregate portion to the coating portion constituting the resin-coated sand of the present invention is preferably 0.2 to 10 parts by mass, more preferably 0.5 to 8 parts by mass, of the coating portion relative to 100 parts by mass of the aggregate portion.

[0063] The method for producing the resin-coated sand of the present invention is not particularly limited, but conventionally known methods such as dry hot coating, semi-hot coating, cold coating, powder solvent method, etc. are applicable. In the present invention, the dry hot coating method is preferred.

[0064] The dry hot coating method involves kneading preheated aggregate with a resin composition for resin-coated sand, followed by cooling the resulting mass of kneaded material with air to break it into granules. The method for using the resin composition for resin-coated sand used in the kneading process is not particularly limited, and examples include kneading a composition containing all components with aggregate, or kneading specific components with aggregate while adding them in portions. Alternatively, other components may be brought into contact with the granules after air cooling. The preheating temperature for the aggregate is preferably a temperature at which the curing reaction of the lignin-modified phenolic resin or phenolic resin does not begin when a curing agent is included in the resin composition for resin-coated sand, and is preferably 100°C to 200°C, more preferably 110°C to 180°C.

[0065] The resin-coated sand of the present invention is suitable as a raw material for producing a shaped product consisting of a hardened molded body by, for example, filling it into a mold for molding using a shell molding method and firing it. The shaped product is preferably a mold (including a core) used to produce parts containing metals or alloys used in various industries.

[0066] When producing a cured molded body, first, the resin-coated sand is filled into a mold using a gravity drop method, a blowing method, or the like, and then the mold is fired. The firing temperature is preferably 150°C or higher, more preferably 200°C to 300°C. The firing time is set appropriately depending on the size or volume of the mold cavity, but is usually 0.5 minutes or longer.

[0067] Next, a process will be described in which a mold and a core for producing castings are produced as hardened molded bodies using the resin-coated sand of the present invention, and then these are used to produce castings (cast products).

[0068] First, molten metal is poured between a foundry mold and a core placed in a predetermined position within the resin-coated sand, and the resin-coated sand is cooled to form a casting. Then, to recover the casting, a vibrator such as a knockout machine is used to vibrate the foundry mold and core, thereby collapsing them. Depending on the shape of the casting, after the cooling, the foundry mold alone may be demolded and vibrated to collapse the core. After collapsing the foundry mold and core, they can be crushed and reused as aggregate. As described above, the resin-coated sand of the present invention contains specific components, and therefore provides hardened molded products such as foundry molds and cores that have excellent shape stability, excellent casting productivity (moldability), and excellent disintegrability after casting production.

[0069] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0070] 1. Production of Resin Composition for Resin-Coated Sand A lignin-modified novolac-type phenolic resin was synthesized using phenol, 47% formalin aqueous solution, oxalic acid, and acetate lignin, soda lignin, or kraft lignin, and then mixed with a lubricant, a coupling agent, and the following disintegrants (1), (2), (3), (4), (5), or (6) to obtain a resin composition for resin-coated sand: (1) Potassium nitrate powder (2) Sodium nitrate powder (3) Magnesium nitrate powder (4) Liquid 1,3-phenylenebis(diphenylphosphate) "CR-733S" (trade name) manufactured by Daihachi Chemical Industry Co., Ltd. (5) Liquid aliphatic phosphate ester "Fyrol PNX" (trade name) manufactured by ICL JAPAN (6) Tetrabromobisphenol A powder

[0071] Example 1-1: 800 parts by weight of phenol, 200 parts by weight (solids content) of acetic acid lignin, 272 parts by weight of 47% formalin, and 4.0 parts by weight of oxalic acid were charged into a reaction vessel equipped with a thermometer, a stirrer, and a condenser. The molar ratio of phenol to formalin (F / P) was 0.50. The raw materials in the reaction vessel were then gradually heated to the reflux temperature (approximately 100°C), and reacted under reflux for 240 minutes. The reaction mixture was then heated and concentrated under reduced pressure until the reaction temperature reached 180°C or higher and the amount of unreacted phenol was less than 1%, yielding a lignin-modified novolac phenolic resin with a modification rate of 20% (hereinafter referred to as "lignin-modified novolac phenolic resin R-1") (see Table 1). After that, 100 parts by mass of the lignin-modified novolac phenolic resin R-1 was slowly cooled to about 170°C, and 3 parts by mass of ethylene bisstearic acid amide (lubricant) and 1 part by mass of 3-aminopropyltriethoxysilane (silane coupling agent) were added and mixed. 10 parts by mass of potassium nitrate powder was then added and mixed to obtain a resin composition for resin-coated sand (hereinafter referred to as "resin composition T-1") (see Table 1).

[0072] Example 1-2: A lignin-modified novolac phenolic resin with a modification rate of 10% (hereinafter referred to as "lignin-modified novolac phenolic resin R-2") was obtained under the same conditions and procedures as in Example 1-1, except that 900 parts by weight of phenol, 100 parts by weight (solids content) of acetic acid lignin, 336 parts by weight of 47% formalin, and 4.0 parts by weight of oxalic acid were used (the molar ratio of phenol to formalin (F / P) was 0.55) (see Table 1). This lignin-modified novolac phenolic resin R-2 was then subjected to the same procedures as in Example 1-1 to obtain a nitrate-containing resin composition for resin-coated sand (hereinafter referred to as "resin composition T-2") (see Table 1).

[0073] Example 1-3: A lignin-modified novolac phenolic resin with a modification rate of 50% (hereinafter referred to as "lignin-modified novolac phenolic resin R-3") was obtained under the same conditions and procedures as in Example 1-1, except that 500 parts by weight of phenol, 500 parts by weight (solids content) of acetic acid lignin, 136 parts by weight of 47% formalin, and 4.0 parts by weight of oxalic acid were used (the molar ratio of phenol to formalin (F / P) was 0.40) (see Table 1). This lignin-modified novolac phenolic resin R-3 was then used in the same manner as in Example 1-1 to obtain a nitrate-containing resin composition for resin-coated sand (hereinafter referred to as "resin composition T-3") (see Table 1).

[0074] Example 1-4: A lignin-modified novolac phenolic resin with a modification rate of 20% (hereinafter referred to as "lignin-modified novolac phenolic resin R-4") was obtained under the same conditions and procedures as in Example 1-1, except that 800 parts by weight of phenol, 200 parts by weight (solids content), 272 parts by weight of 47% formalin, and 4.0 parts by weight of oxalic acid were used (the molar ratio of phenol to formalin (F / P) was 0.50) (see Table 1). This lignin-modified novolac phenolic resin R-4 was then used in the same manner as in Example 1-1 to obtain a nitrate-containing resin composition for resin-coated sand (hereinafter referred to as "resin composition T-4") (see Table 1).

[0075] Example 1-5: A lignin-modified novolac phenolic resin with a modification rate of 10% (hereinafter referred to as "lignin-modified novolac phenolic resin R-5") was obtained under the same conditions and procedures as in Example 1-1, except that 900 parts by weight of phenol, 100 parts by weight (solids content) of soda lignin, 336 parts by weight of 47% formalin, and 4.0 parts by weight of oxalic acid were used (the molar ratio of phenol to formalin (F / P) was 0.55) (see Table 1). This lignin-modified novolac phenolic resin R-5 was then used in the same manner as in Example 1-1 to obtain a nitrate-containing resin composition for resin-coated sand (hereinafter referred to as "resin composition T-5") (see Table 1).

[0076] Example 1-6: A lignin-modified novolac phenolic resin with a modification rate of 50% (hereinafter referred to as "lignin-modified novolac phenolic resin R-6") was obtained under the same conditions and procedures as in Example 1-1, except that 500 parts by weight of phenol, 500 parts by weight (solids content) of soda lignin, 136 parts by weight of 47% formalin, and 4.0 parts by weight of oxalic acid were used (the molar ratio of phenol to formalin (F / P) was 0.40) (see Table 1). This lignin-modified novolac phenolic resin R-6 was then subjected to the same procedures as in Example 1-1 to obtain a nitrate-containing resin composition for resin-coated sand (hereinafter referred to as "resin composition T-6") (see Table 1).

[0077] Example 1-7: A lignin-modified novolac phenolic resin with a modification rate of 20% (hereinafter referred to as "lignin-modified novolac phenolic resin R-7") was obtained under the same conditions and procedures as in Example 1-1, except that 800 parts by weight of phenol, 200 parts by weight (solids), 272 parts by weight of 47% formalin, and 4.0 parts by weight of oxalic acid were used (the molar ratio of phenol to formalin (F / P) was 0.50) (see Table 1). This lignin-modified novolac phenolic resin R-7 was then subjected to the same procedures as in Example 1-1 to obtain a nitrate-containing resin composition for resin-coated sand (hereinafter referred to as "resin composition T-7") (see Table 1).

[0078] Example 1-8: A lignin-modified novolac phenolic resin with a modification rate of 10% (hereinafter referred to as "lignin-modified novolac phenolic resin R-8") was obtained under the same conditions and procedures as in Example 1-1, except that 900 parts by weight of phenol, 100 parts by weight (solids content), 336 parts by weight of 47% formalin, and 4.0 parts by weight of oxalic acid were used (the molar ratio of phenol to formalin (F / P) was 0.55) (see Table 1). This lignin-modified novolac phenolic resin R-8 was then subjected to the same procedures as in Example 1-1 to obtain a nitrate-containing resin composition for resin-coated sand (hereinafter referred to as "resin composition T-8") (see Table 1).

[0079] Example 1-9: A lignin-modified novolac phenolic resin with a modification rate of 50% (hereinafter referred to as "lignin-modified novolac phenolic resin R-9") was obtained under the same conditions and procedures as in Example 1-1, except that 500 parts by weight of phenol, 500 parts by weight (solids content), 136 parts by weight of 47% formalin, and 4.0 parts by weight of oxalic acid were used (the molar ratio of phenol to formalin (F / P) was 0.40) (see Table 1). This lignin-modified novolac phenolic resin R-9 was then subjected to the same procedures as in Example 1-1 to obtain a nitrate-containing resin composition for resin-coated sand (hereinafter referred to as "resin composition T-9") (see Table 1).

[0080] Example 1-10 In Example 1-1, the reaction solution containing the lignin-modified novolac phenolic resin R-1 was concentrated under reduced pressure and then slowly cooled to about 170°C. To 100 parts by mass of the lignin-modified novolac phenolic resin R-1, 3 parts by mass of ethylene bisstearic acid amide (lubricant) and 1 part by mass of 3-aminopropyltriethoxysilane (silane coupling agent) were added and mixed. Furthermore, 5 parts by mass of potassium nitrate powder was added to 100 parts by mass of the lignin-modified novolac phenolic resin R-1, and the mixture was mixed to obtain a resin composition for resin-coated sand (hereinafter referred to as "resin composition T-10") (see Table 2).

[0081] Example 1-11 The same procedure as in Example 1-10 was carried out, except that the lignin-modified novolac phenolic resin R-4 synthesized in Example 1-4 was used instead of the lignin-modified novolac phenolic resin R-1, to obtain a resin composition for resin-coated sand containing nitrate (hereinafter referred to as "resin composition T-11") (see Table 2).

[0082] Example 1-12 The same procedure as in Example 1-10 was carried out, except that the lignin-modified novolac phenolic resin R-5 synthesized in Example 1-5 was used instead of the lignin-modified novolac phenolic resin R-1, to obtain a resin composition for resin-coated sand containing nitrate (hereinafter referred to as "resin composition T-12") (see Table 2).

[0083] Example 1-13 The same procedure as in Example 1-10 was carried out, except that the lignin-modified novolac phenolic resin R-6 synthesized in Example 1-6 was used instead of the lignin-modified novolac phenolic resin R-1, to obtain a resin composition for resin-coated sand containing nitrate (hereinafter referred to as "resin composition T-13") (see Table 2).

[0084] Example 1-14 The same procedure as in Example 1-10 was carried out, except that the lignin-modified novolac phenolic resin R-7 synthesized in Example 1-7 was used instead of the lignin-modified novolac phenolic resin R-1, to obtain a resin composition for resin-coated sand containing nitrate (hereinafter referred to as "resin composition T-14") (see Table 2).

[0085] Example 1-15 The same procedure as in Example 1-1 was carried out except that sodium nitrate powder was used instead of potassium nitrate powder, to obtain a resin composition for resin-coated sand containing nitrate (hereinafter referred to as "resin composition T-15") (see Table 2).

[0086] Example 1-16 The same procedure as in Example 1-1 was carried out except that magnesium nitrate powder was used instead of potassium nitrate powder, to obtain a resin composition for resin-coated sand containing nitrate (hereinafter referred to as "resin composition T-16") (see Table 2).

[0087] Example 1-17 The same procedure as in Example 1-1 was carried out, except that an aromatic phosphate ester liquid was used instead of potassium nitrate powder, to obtain a resin composition for resin-coated sand containing nitrate (hereinafter referred to as "resin composition T-17") (see Table 2).

[0088] Example 1-18 The same procedure as in Example 1-1 was carried out, except that an aliphatic phosphate ester liquid was used instead of the potassium nitrate powder, to obtain a resin composition for resin-coated sand containing an aliphatic phosphate ester (hereinafter referred to as "resin composition T-18") (see Table 2).

[0089] Example 1-19 The same procedure as in Example 1-1 was carried out, except that aliphatic phosphate ester liquid was used instead of potassium nitrate powder, and the lignin-modified novolac phenolic resin R-2 obtained in Example 1-2 was used instead of the lignin-modified novolac phenolic resin R-1, to obtain a resin composition for resin-coated sand containing aliphatic phosphate ester (hereinafter referred to as "resin composition T-19") (see Table 2).

[0090] Example 1-20 The same procedure as in Example 1-1 was carried out, except that aliphatic phosphate ester liquid was used instead of potassium nitrate powder and lignin-modified novolac phenolic resin R-3 obtained in Example 1-3 was used instead of lignin-modified novolac phenolic resin R-1, to obtain a resin composition for resin-coated sand containing aliphatic phosphate ester (hereinafter referred to as "resin composition T-20") (see Table 2).

[0091] Comparative Example 1-1: 1,000 parts by mass of phenol, 475 parts by mass of 47% formalin, and 5.0 parts by mass of oxalic acid were charged into a reaction vessel equipped with a thermometer, a stirrer, and a condenser. The molar ratio of phenol to formalin (F / P) was 0.70. The raw materials in the reaction vessel were then gradually heated to the reflux temperature (approximately 100°C), and reacted under reflux for 240 minutes. The reaction mixture was then heated and concentrated under reduced pressure until the reaction temperature reached 180°C or higher and the amount of unreacted phenol was less than 1%, yielding an unmodified novolac phenolic resin (hereinafter referred to as "unmodified novolac phenolic resin S-1") (see Table 3). After that, 100 parts by mass of the unmodified novolac phenolic resin S-1 was slowly cooled to about 170°C, and 3 parts by mass of ethylene bisstearic acid amide (lubricant) and 1 part by mass of 3-aminopropyltriethoxysilane (silane coupling agent) were added and mixed, respectively, to obtain a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-1") (see Table 3).

[0092] Comparative Example 1-2 To the resin composition TT-1 obtained in Comparative Example 1-1, 10 parts by mass of potassium nitrate powder was further added and mixed to obtain a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-2") (see Table 3).

[0093] Comparative Example 1-3 5 parts by mass of potassium nitrate powder was further added to the resin composition TT-1 obtained in Comparative Example 1-1 and mixed to obtain a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-3") (see Table 3).

[0094] Comparative Example 1-4 In Comparative Example 1-1, the reaction solution containing the unmodified novolac phenolic resin S-1 was concentrated under reduced pressure and then slowly cooled to about 170°C. To 100 parts by mass of the unmodified novolac phenolic resin S-1, 3 parts by mass of ethylene bisstearic acid amide (lubricant) and 1 part by mass of 3-aminopropyltriethoxysilane (silane coupling agent) were added and mixed. Furthermore, 10 parts by mass of tetrabromobisphenol A powder was added to 100 parts by mass of the unmodified novolac phenolic resin S-1, and the mixture was mixed to obtain a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-4") (see Table 3).

[0095] Comparative Example 1-5 In Comparative Example 1-1, the reaction solution containing the unmodified novolac phenolic resin S-1 was concentrated under reduced pressure and then slowly cooled to about 170°C. To 100 parts by mass of the unmodified novolac phenolic resin S-1, 3 parts by mass of ethylene bisstearic acid amide (lubricant) and 1 part by mass of 3-aminopropyltriethoxysilane (silane coupling agent) were added and mixed. Furthermore, 5 parts by mass of tetrabromobisphenol A powder was added to 100 parts by mass of the unmodified novolac phenolic resin S-1, and the mixture was mixed to obtain a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-5") (see Table 3).

[0096] Comparative Example 1-6 In Example 1-1, the resin composition before adding the potassium nitrate powder was used as a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-6") (see Table 4).

[0097] Comparative Example 1-7 In Example 1-2, the resin composition before adding the potassium nitrate powder was used as a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-7") (see Table 4).

[0098] Comparative Example 1-8 In Example 1-3, the resin composition before adding the potassium nitrate powder was used as a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-8") (see Table 4).

[0099] Comparative Example 1-9 In Example 1-4, the resin composition before adding the potassium nitrate powder was used as a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-9") (see Table 4).

[0100] Comparative Example 1-10 In Example 1-5, the resin composition before adding the potassium nitrate powder was used as a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-10") (see Table 4).

[0101] Comparative Example 1-11 In Example 1-6, the resin composition before adding the potassium nitrate powder was used as a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-11") (see Table 4).

[0102] Comparative Example 1-12 In Example 1-7, the resin composition before adding the potassium nitrate powder was used as a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-12") (see Table 4).

[0103] Comparative Example 1-13 In Example 1-8, the resin composition before adding the potassium nitrate powder was used as a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-13") (see Table 4).

[0104] Comparative Example 1-14 In Example 1-9, the resin composition before adding the potassium nitrate powder was used as a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-14") (see Table 4).

[0105] Comparative Example 1-15 A resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-15") was obtained by performing the same operation as in Example 1-1, except that 10 parts by mass of tetrabromobisphenol A powder was used instead of 10 parts by mass of potassium nitrate powder (see Table 5).

[0106] Comparative Example 1-16 A resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-16") was obtained by performing the same operation as in Example 1-2, except that 10 parts by mass of tetrabromobisphenol A powder was used instead of 10 parts by mass of potassium nitrate powder (see Table 5).

[0107] Comparative Example 1-17 A resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-17") was obtained in the same manner as in Example 1-3, except that 10 parts by mass of tetrabromobisphenol A powder was used instead of 10 parts by mass of potassium nitrate powder (see Table 5).

[0108] Comparative Example 1-18 A resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-18") was obtained by performing the same operation as in Example 1-4, except that 10 parts by mass of tetrabromobisphenol A powder was used instead of 10 parts by mass of potassium nitrate powder (see Table 5).

[0109] Comparative Example 1-19 A resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-19") was obtained by performing the same operation as in Example 1-5, except that 10 parts by mass of tetrabromobisphenol A powder was used instead of 10 parts by mass of potassium nitrate powder (see Table 5).

[0110] Comparative Example 1-20 A resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-20") was obtained by performing the same operation as in Example 1-6, except that 10 parts by mass of tetrabromobisphenol A powder was used instead of 10 parts by mass of potassium nitrate powder (see Table 5).

[0111] Comparative Example 1-21 A resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-21") was obtained in the same manner as in Example 1-7, except that 10 parts by mass of tetrabromobisphenol A powder was used instead of 10 parts by mass of potassium nitrate powder (see Table 5).

[0112] Comparative Example 1-22 A resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-22") was obtained in the same manner as in Example 1-8, except that 10 parts by mass of tetrabromobisphenol A powder was used instead of 10 parts by mass of potassium nitrate powder (see Table 5).

[0113] Comparative Example 1-23 A resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-23") was obtained by performing the same operation as in Example 1-9, except that 10 parts by mass of tetrabromobisphenol A powder was used instead of 10 parts by mass of potassium nitrate powder (see Table 5).

[0114] Comparative Example 1-24 To the resin composition TT-1 obtained in Comparative Example 1-1, 10 parts by mass of aliphatic phosphate ester liquid was further added and mixed to obtain a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-24") (see Table 5).

[0115]

[0116]

[0117]

[0118]

[0119]

[0120] 2. Production and Evaluation of Resin-Coated Sand (1) Resin-coated sand was produced using each of the resin compositions for resin-coated sand obtained in Examples 1-1 to 1-20 and Comparative Examples 1-1 to 1-24, Australian natural silica sand "Flattery Sand" (product name, AFS index: 60), a curing agent (hexamethylenetetramine), and a lubricant (calcium stearate).

[0121] Example 2-1: 105 parts by weight of resin composition T-1 shown in Table 1 and 7,000 parts by weight of natural silica sand heated to 150°C were added to a laboratory Whirl mixer and kneaded for 60 seconds. Next, an aqueous solution of 15.8 parts by weight of hexamethylenetetramine dissolved in 105 parts by weight of water was added, and the resulting mixture was cooled by blowing air and kneaded until the aggregates disintegrated into granules. Seven parts by weight of calcium stearate was then added and kneaded. This resulted in a resin-coated sand (hereinafter referred to as "RCS-1") in which the surface of natural silica sand was coated with a resin composition for resin-coated sand containing a lignin-modified novolac phenolic resin, a lubricant, a curing agent, a silane coupling agent, and a nitrate (see Table 6).

[0122] A mold was then formed using this RCS-1, and a molten metal or other material was poured into the mold to conduct an experiment (measurement of the collapse rate) to confirm the collapse of the mold after the casting was formed. The results are shown in Table 6.

[0123] <Disintegration Rate Measurement> According to a method conforming to JIS K 6910, 50 grams of RCS-1 was filled into a mold temperature-controlled at 250°C and molded for 60 seconds to produce five JIS-type test pieces (cured molded product, size: 10 mm x 10 mm x 60 mm). These test pieces were then double-wrapped with two sheets of aluminum foil to prepare a package. The package was then placed in a furnace heated to 400°C and heated for 30 minutes, at which point the five test pieces were removed and allowed to cool naturally to room temperature. The flexural strength of the test pieces before and after this heat treatment was measured using a digital molding sand strength tester "SC-200D-B" (model name) manufactured by Tokai SE Co., Ltd. at a measurement speed (head speed): 10 mm / min. The flexural strength (%) was calculated from the average values ​​of the flexural strength before and after the heat treatment using the following formula: Disintegration rate = [(flexural strength before heat treatment - flexural strength after heat treatment) / flexural strength before heat treatment] x 100. A higher disintegration rate means better mold disintegrability. The disintegrability was evaluated based on the calculated values ​​according to the following criteria: ◎: 70% or more ◯: 60% or more but less than 70% △: Less than 60%

[0124] Examples 2-2 to 2-14 and 2-18 to 2-23 The same procedure as in Example 2-1 was carried out, except that resin compositions T-2 to T-14 and T-18 to T-23 were used instead of resin composition T-1. Resin-coated sands (hereinafter referred to as "RCS-2" to "RCS-14" and "RCS-18" to "RCS-23", respectively) were obtained, in which the surface of natural silica sand was coated with a resin composition containing a lignin-modified novolac phenolic resin, a lubricant, a curing agent, a silane coupling agent, and a nitrate (see Tables 6, 7, and 8). Then, disintegration rates were measured, and the results are shown in Tables 6, 7, and 8.

[0125] Example 2-15: 105 parts by weight of the resin composition TT-6 obtained in Comparative Example 1-6, 10.5 parts by weight of potassium nitrate powder, and 7,000 parts by weight of natural silica sand heated to 150°C were added to a laboratory Whirl mixer and kneaded for 60 seconds. Next, an aqueous solution prepared by dissolving 15.8 parts by weight of hexamethylenetetramine in 105 parts by weight of water was added, and the resulting mixture was cooled by blowing air and kneaded until the aggregates disintegrated into granules. Seven parts by weight of calcium stearate was then added and kneaded. This resulted in a resin-coated sand (hereinafter referred to as "RCS-15") in which the surface of natural silica sand was coated with a resin composition for resin-coated sand containing a lignin-modified novolac phenolic resin, a lubricant, a curing agent, a silane coupling agent, and a nitrate (see Table 7).

[0126] Examples 2-16 and 2-17 The same procedures as in Example 2-15 were carried out except that resin compositions TT-9 and TT-12 were used instead of resin composition TT-6, to obtain resin-coated sands (hereinafter referred to as "RCS-16" and "RCS-17", respectively) in which the surface of natural silica sand was coated with a resin composition for resin-coated sand containing a lignin-modified novolak-type phenolic resin, a lubricant, a curing agent, a silane coupling agent, and a nitrate (see Table 7).

[0127] Example 2-24 The same procedure as in Example 2-15 was carried out, except that an aliphatic phosphate ester liquid was used instead of the potassium nitrate powder, to obtain resin-coated sand (hereinafter referred to as "RCS-24") in which the surface of natural silica sand was coated with a resin composition for resin-coated sand containing a lignin-modified novolac-type phenolic resin, a lubricant, a curing agent, a silane coupling agent, and an aliphatic phosphate ester (see Table 8).

[0128] Comparative Examples 2-1 to 2-23 and 2-29 Instead of resin composition T-1, resin compositions TT-1 to TT-23 and TT-24 were used. The same operation as in Example 2-1 was performed, and a resin composition for resin-coated sand containing a lignin-modified novolac phenolic resin, a lubricant, a curing agent, and a silane coupling agent was obtained. Alternatively, a resin composition for resin-coated sand containing a non-modified novolac phenolic resin, a lubricant, a curing agent, a silane coupling agent, and tetrabromobisphenol A was obtained. Alternatively, a resin composition for resin-coated sand containing a lignin-modified novolac phenolic resin, a lubricant, a curing agent, a silane coupling agent, and tetrabromobisphenol A was obtained. Alternatively, a resin composition for resin-coated sand containing a non-modified novolac phenolic resin, a lubricant, a curing agent, a silane coupling agent, and an aliphatic phosphate ester was obtained. The resin-coated sand (hereinafter referred to as "RCS-1E" to "RCS-23E" and "RCS-29E") was obtained. (See Tables 9 and 8.) Thereafter, the disintegration rate was measured, and the results are shown in Tables 9, 10, 11 and 12.

[0129] Comparative Example 2-24 The same procedure as in Example 2-15 was carried out, except that resin composition TT-1 was used instead of resin composition TT-6, to obtain resin-coated sand (hereinafter referred to as "RCS-24E") in which the surface of natural silica sand was coated with a resin composition for resin-coated sand containing an unmodified novolac phenolic resin, a lubricant, a curing agent, and a silane coupling agent (see Table 12). Thereafter, the disintegration rate was measured, and the results are also shown in Table 12.

[0130] Comparative Example 2-25: 105 parts by mass of the resin composition TT-1 obtained in Comparative Example 1-1, 10.5 parts by mass of tetrabromobisphenol A powder, and 7,000 parts by mass of natural silica sand heated to 150°C were added to a laboratory Whirl mixer and kneaded for 60 seconds. Next, an aqueous solution prepared by dissolving 15.8 parts by mass of hexamethylenetetramine in 105 parts by mass of water was added, and the resulting mixture was cooled by blowing air and kneaded until the aggregates disintegrated into granules. Seven parts by mass of calcium stearate was then added and kneaded. This resulted in a resin-coated sand (hereinafter referred to as "RCS-25E") in which the surface of natural silica sand was coated with a resin composition for resin-coated sand containing an unmodified novolac phenolic resin, a lubricant, a curing agent, a silane coupling agent, and tetrabromobisphenol A (see Table 12). The disintegration rate was then measured, and the results are shown in Table 12.

[0131] Comparative Examples 2-26 to 2-28 The same procedure as in Comparative Example 2-25 was carried out, except that resin compositions TT-6, TT-9, and TT-12 were used instead of resin composition TT-1, to obtain resin-coated sands (hereinafter referred to as "RCS-26E" to "RCS-28E," respectively) in which the surface of natural silica sand was coated with a resin composition for resin-coated sand containing a lignin-modified novolac-type phenolic resin, a lubricant, a curing agent, a silane coupling agent, and tetrabromobisphenol A (see Table 12). Subsequently, disintegration rates were measured, and the results are also shown in Table 12.

[0132] Comparative Example 2-30: The same procedure as in Comparative Example 2-25 was carried out, except that an aliphatic phosphate ester liquid was used instead of tetrabromobisphenol A powder, to obtain resin-coated sand (hereinafter referred to as "RCS-30E") in which the surface of natural silica sand was coated with a resin composition for resin-coated sand containing a lignin-modified novolac-type phenolic resin, a lubricant, a curing agent, a silane coupling agent, and an aliphatic phosphate ester (see Table 9). The disintegration rate was then measured, and the results are shown in Table 12.

[0133]

[0134]

[0135]

[0136]

[0137]

[0138]

[0139]

[0140] The following can be seen from Tables 6 to 12: Examples 2-1 to 2-24 having the configuration of the present invention had higher disintegration rates than Comparative Examples 2-1 to 2-30, i.e., the cases in which nitrate, aliphatic phosphate ester, or tetrabromobisphenol A as a disintegrant was combined with a non-modified phenolic resin, and the cases in which tetrabromobisphenol A was combined with a lignin-modified phenolic resin.

[0141] 3. Production and Evaluation of Resin-Coated Sand (2) Resin-coated sand containing unmodified phenolic resin, lignin, and nitrate was produced.

[0142] Example 3-1: 84 parts by weight of the resin composition TT-1 shown in Table 3, 21 parts by weight of acetic acid lignin, 10.5 parts by weight of potassium nitrate powder, and 7,000 parts by weight of natural silica sand heated to 150°C were added to a laboratory Whirl mixer and kneaded for 60 seconds. Next, an aqueous solution of 15.8 parts by weight of hexamethylenetetramine dissolved in 105 parts by weight of water was added, and the resulting mixture was cooled by blowing air and kneaded until the aggregates disintegrated into granules. Seven parts by weight of calcium stearate was then added and kneaded. This resulted in a resin-coated sand (hereinafter referred to as "RCS-51") in which the surface of natural silica sand was coated with a resin composition for resin-coated sand containing an unmodified novolac-type phenolic resin, a lubricant, a curing agent, a silane coupling agent, and a nitrate (see Table 13). The disintegration rate was then measured, and the results are shown in Table 13.

[0143] Comparative Example 3-1: 84 parts by weight of the resin composition TT-1 shown in Table 3, 21 parts by weight of acetic acid lignin, and 7,000 parts by weight of natural silica sand heated to 150°C were added to a laboratory Whirl mixer and kneaded for 60 seconds. Next, an aqueous solution of 15.8 parts by weight of hexamethylenetetramine dissolved in 105 parts by weight of water was added, and the resulting mixture was cooled by blowing air and kneaded until the aggregates disintegrated into granules. Seven parts by weight of calcium stearate was then added and kneaded. This resulted in a resin-coated sand (hereinafter referred to as "RCS-51E") in which the surface of natural silica sand was coated with a resin composition for resin-coated sand containing an unmodified novolac-type phenolic resin, a lubricant, a curing agent, a silane coupling agent, and a nitrate (see Table 13). The disintegration rate was then measured, and the results are shown in Table 13.

[0144] Comparative Example 3-2: 84 parts by weight of the resin composition TT-1 shown in Table 3, 21 parts by weight of acetic acid lignin, 10.5 parts by weight of tetrabromobisphenol A powder, and 7,000 parts by weight of natural silica sand heated to 150°C were added to a laboratory Whirl mixer and kneaded for 60 seconds. Next, an aqueous solution of 15.8 parts by weight of hexamethylenetetramine dissolved in 105 parts by weight of water was added, and the resulting mixture was cooled by blowing air and kneaded until the aggregates disintegrated into granules. Seven parts by weight of calcium stearate was then added and kneaded. This resulted in a resin-coated sand (hereinafter referred to as "RCS-52E") in which the surface of natural silica sand was coated with a resin composition for resin-coated sand containing an unmodified novolac phenolic resin, a lubricant, a curing agent, a silane coupling agent, a nitrate, and tetrabromobisphenol A (see Table 13). The disintegration rate was then measured, and the results are shown in Table 13.

[0145]

[0146] The following can be seen from Table 13: Example 3-1 having the configuration of the present invention had a higher disintegration rate than both Comparative Examples 3-1 and 3-2, i.e., the case where a non-modified phenolic resin and lignin were combined without containing nitrate as a disintegrant, and the case where tetrabromobisphenol A as a disintegrant, a non-modified phenolic resin, and lignin were combined.

[0147] By using the resin composition for resin-coated sand of the present invention together with aggregate, resin-coated sand suitable for producing casting molds and the like can be obtained. Furthermore, when the resin-coated sand of the present invention is subjected to, for example, a shell molding method to produce a casting, the resulting mold exhibits excellent disintegration properties. Therefore, parts containing metals or alloys used in various industries can be efficiently produced.

Claims

1. A resin composition for resin-coated sand, which is used in the production of resin-coated sand, and which contains at least one of a lignin-modified phenolic resin and a mixture of lignin and a phenolic resin, and a nitrate.

2. A resin composition for resin-coated sand, which is used in the production of resin-coated sand, and which contains at least one of a lignin-modified phenolic resin and a mixture of lignin and a phenolic resin, and a phosphoric acid ester.

3. A resin composition for resin-coated sand according to claim 1 or 2, wherein the lignin-modified phenolic resin is a reaction product of at least one lignin selected from kraft lignin, soda lignin and acetic acid lignin, a phenol, and an aldehyde.

4. A resin composition for resin-coated sand according to any one of claims 1 to 3, further comprising a curing agent.

5. A resin composition for resin-coated sand according to any one of claims 1 to 4, further comprising a lubricant.

6. A resin composition for resin-coated sand according to any one of claims 1 to 5, further comprising a silane coupling agent.

7. A resin composition for resin-coated sand according to claim 1, 3, 4, 5 or 6, wherein the nitrate is an alkali metal salt or an alkaline earth metal salt.

8. A resin composition for resin-coated sand according to claim 7, wherein the nitrate is potassium nitrate.

9. A resin composition for resin-coated sand according to any one of claims 2 to 6, wherein the phosphate ester is an aliphatic phosphate ester.

10. Resin-coated sand comprising at least one of a lignin-modified phenolic resin and a mixture of lignin and a phenolic resin, a nitrate, and an aggregate.

11. The resin-coated sand according to claim 10, wherein at least a portion of the surface of the aggregate is coated with a composition containing at least one of the lignin-modified phenolic resin and the mixture of lignin and phenolic resin, and the nitrate.

12. Resin-coated sand comprising at least one of a lignin-modified phenolic resin and a mixture of lignin and a phenolic resin, a phosphate ester, and an aggregate.

13. The resin-coated sand according to claim 12, wherein at least a portion of the surface of the aggregate is coated with a composition containing at least one of the lignin-modified phenolic resin and the mixture of lignin and phenolic resin, and the phosphate ester.

14. Resin-coated sand according to claim 12 or 13, wherein the phosphate ester is an aliphatic phosphate ester.

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