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

Abstract

A resin composition for resin-coated sand according to 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, and having a sulfur content of 1,000 ppm or less. The resin composition may further contain a curing agent, a lubricant, a silane coupling agent, and the like. A resin-coated sand according to the present invention contains the resin composition for resin-coated sand and an aggregate. It is preferable that at least a part of the surface of the aggregate is coated with the resin composition for resin-coated sand.

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 for the binder (see, for example, Patent Documents 1 and 2).

[0003] International Publication No. 2019 / 142488 International Publication No. 2023 / 223996

[0004] An object of the present invention is to provide resin-coated sand that can suppress the emission of unpleasant sulfur-based gases when the resin-coated sand filled into a mold for molding is baked and then the mold is opened to recover the resulting hardened molded body, and a resin composition for resin-coated sand that can be used in the production of the resin-coated sand.

[0005] The present inventors have discovered that the above-mentioned problems can be solved by filling a mold with resin-coated sand obtained using a resin composition containing a lignin-modified phenolic resin or a mixture of lignin and phenolic resin and having a sulfur content of 1000 ppm or less, and then firing the resulting sand.

[0006] The present invention is described below. [1] A resin composition for use in producing resin-coated sand, comprising at least one of a lignin-modified phenolic resin and a mixture of lignin and a phenolic resin, and having a sulfur content of 1,000 ppm or less. [2] The resin composition for resin-coated sand according to [1] above, wherein the lignin-modified phenolic resin is a reaction product of kraft lignin, a phenol, and an aldehyde. [3] The resin composition for resin-coated sand according to [1] above, wherein the lignin-modified phenolic resin is a reaction product of soda lignin or acetic acid lignin, a phenol, and an aldehyde. [4] The resin composition for resin-coated sand according to any one of [1] to [3] above, further comprising a curing agent. [5] The resin composition for 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] Resin-coated sand, characterized by comprising the resin composition for resin-coated sand according to any one of [1] to [6] above and aggregate. [8] The resin-coated sand according to [7] above, in which at least a portion of the surface of the aggregate is coated with the resin composition for resin-coated sand.

[0007] According to the present invention, when the resin-coated sand of the present invention filled into a mold for molding is baked and then the mold is opened to recover the resulting cured molded body, the emission of unpleasant sulfur-based gases can be suppressed, thereby suppressing problems such as a deterioration in the working environment. The resin composition for resin-coated sand of the present invention is suitable for forming such resin-coated sand.

[0008] 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.

[0009] 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 a shaped article consisting of a cured molded body by filling it into 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), and having a sulfur content of 1000 ppm or less. The resin composition for resin-coated sand of the present invention can further contain other components (described below) as necessary.

[0010] 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.

[0011] Lignin-modified phenolic resins are reaction products of lignin, phenols, and aldehydes.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.).

[0018] 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.

[0019] 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.

[0020] 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.

[0021] In the present invention, kraft lignin, soda lignin, acetic acid lignin, etc. are preferably used as the lignin.

[0022] 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.

[0023] 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.

[0024] When aldehydes are reacted with lignin and phenols, an aqueous solution of the aldehydes can be used.

[0025] 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 1,900 parts by mass, more preferably 100 to 900 parts by mass, based on 100 parts by mass of lignin. When the lignin is kraft lignin, the amount of phenols used is preferably 1,150 to 1,900 parts by mass, more preferably 1,330 to 1,900 parts by mass, based on 100 parts by mass of kraft lignin. When the lignin is soda lignin or acetic acid lignin, the amount of phenols used is preferably 100 to 1,900 parts by mass, more preferably 100 to 900 parts by mass, based on 100 parts by mass of soda lignin or acetic acid lignin. The amount of aldehydes used is preferably 10 to 500 parts by mass, more preferably 10 to 400 parts by mass, based on 100 parts by mass of lignin used.

[0026] 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.

[0027] The amount of the acid catalyst used is preferably 0.1 to 3 parts by mass, more preferably 0.2 to 2 parts by mass, based on 100 parts by mass of the amount of the phenol used.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The lignin modification rate in the lignin-modified phenolic resin according to the present invention is preferably 5 to 50%, more preferably 10 to 50%, 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

[0032] 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.

[0033] The resin composition for resin-coated sand of the present invention may contain one or more types of lignin-modified phenolic resins.

[0034] In the present invention, a mixture of lignin and a phenolic resin (a phenolic resin that is not modified with lignin, hereinafter simply referred to as a "phenolic resin") can be used instead of a lignin-modified phenolic resin. The lignin can include 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, resol-type phenolic resin, or the like, and of these, novolac-type phenolic resin is preferred.

[0035] 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 calculated on a polystyrene basis by GPC is preferably 200 to 2,000, more preferably 300 to 1,500.

[0036] In the present invention, the content ratios of the lignin and the phenolic resin are preferably 5 to 50% by mass and 50 to 95% by mass, more preferably 10 to 50% by mass and 50 to 90% by mass, respectively, when the total of the two is 100% by mass.

[0037] 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 disintegration improver, 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.

[0038] 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. Additives effective in 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.

[0039] 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 mixture of lignin and phenolic resin.

[0040] 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.

[0041] 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 mixture of lignin and phenolic resin.

[0042] 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.

[0043] 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 mixture of lignin and phenolic resin.

[0044] Examples of the release agent include a fluorine-based release agent and a silicone-based release agent.

[0045] The resin composition for resin-coated sand of the present invention is used together with aggregate to produce resin-coated sand, which is then used to prepare a mold. After a casting is produced using this mold, the mold becomes unnecessary and is destroyed by vibration or the like. However, a disintegration improver can be used as a component to promote the disintegration of the mold. A halogen compound or the like can be used as this disintegration improver.

[0046] 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 particles, mica, vermiculite, iron sand, red iron oxide, and deodorants.

[0047] The resin composition for resin-coated sand of the present invention has a sulfur content of 1000 ppm or less, preferably 900 ppm or less, more preferably 850 ppm or less, and particularly preferably 750 ppm or less. Therefore, not only when resin-coated sand is produced using the resin composition for resin-coated sand of the present invention and aggregate, but also when resin-coated sand is filled into a mold for producing a cured molded body using the resin-coated sand, and then the mold is opened to recover the resulting cured molded body, the emission of unpleasant sulfur-based gases can be suppressed, thereby preventing problems such as a deterioration in the working environment. The method for analyzing the sulfur content is not particularly limited, and for example, fluorescent X-ray analysis can be used.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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. 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] When producing a cured molded body, resin-coated sand is first filled into a mold using a gravity drop method, a blowing method, or the like, and then 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. In the present invention, a cured molded body is produced using resin-coated sand containing a resin composition for resin-coated sand with a sulfur content of 1000 ppm. Therefore, when the mold is opened to obtain the cured molded body, the emission of unpleasant sulfur-based gas odors can be suppressed, and a good working environment can be maintained.

[0057] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0058] 1. Synthesis of Phenolic Resin A lignin-modified novolac-type phenolic resin was synthesized using phenol, a 47% aqueous solution of formalin, oxalic acid, and kraft lignin, soda lignin, or acetic acid lignin.

[0059] Synthesis Example 1: 750 parts by mass of phenol, 250 parts by mass (solids content) of kraft lignin, 255 parts by mass of 47% formalin, and 3.8 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 0.50. The raw materials in the reaction vessel were then gradually heated to a 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 25% (hereinafter referred to as "lignin-modified novolac phenolic resin R-1") (see Table 1).

[0060] The number average molecular weight (Mn) of the obtained lignin-modified novolak phenolic resin R-1 was measured by GPC under the following conditions and was found to be 675 in terms of standard polystyrene (see Table 1). <GPC measurement conditions> Apparatus: "Gel filtration chromatograph SC-8320 series build-up system" manufactured by Tosoh Corporation Column: "G1000H" manufactured by Tosoh Corporation ＸＬ " + "G2000H ＸＬ Detector: Refractive index (RI) Carrier: Tetrahydrofuran Flow rate: 1 mL / min Column temperature: 40°C

[0061] Synthesis Example 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 by the same method as in Synthesis Example 1, except that 900 parts by mass of phenol, 100 parts by mass (solid content) of kraft lignin, 336 parts by mass of 47% formalin, and 3.8 parts by mass of oxalic acid were used (see Table 1).

[0062] Synthesis Example 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 by the same method as in Synthesis Example 1, except that 500 parts by mass of phenol, 500 parts by mass (solid content) of kraft lignin, 136 parts by mass of 47% formalin, and 3.8 parts by mass of oxalic acid were used (see Table 1).

[0063] Synthesis Example 4 A lignin-modified novolac phenolic resin with a modification rate of 5% (hereinafter referred to as "lignin-modified novolac phenolic resin R-4") was obtained under the same conditions and by the same method as in Synthesis Example 1, except that 950 parts by mass of phenol, 50 parts by mass (solid content) of kraft lignin, 387 parts by mass of 47% formalin, and 3.8 parts by mass of oxalic acid were used (see Table 1).

[0064] Synthesis Example 5 A lignin-modified novolac phenolic resin with a modification rate of 25% (hereinafter referred to as "lignin-modified novolac phenolic resin R-5") was obtained under the same conditions and by the same method as in Synthesis Example 1, except that 750 parts by mass of phenol, 250 parts by mass (solid content) of soda lignin, 255 parts by mass of 47% formalin, and 3.8 parts by mass of oxalic acid were used (see Table 1).

[0065] Synthesis Example 6 A lignin-modified novolac phenolic resin with a modification rate of 5% (hereinafter referred to as "lignin-modified novolac phenolic resin R-6") was obtained under the same conditions and by the same method as in Synthesis Example 1, except that 950 parts by mass of phenol, 50 parts by mass (solid content) of soda lignin, 387 parts by mass of 47% formalin, and 3.8 parts by mass of oxalic acid were used (see Table 1).

[0066] Synthesis Example 7 A lignin-modified novolac phenolic resin with a modification rate of 50% (hereinafter referred to as "lignin-modified novolac phenolic resin R-7") was obtained under the same conditions and by the same method as in Synthesis Example 1, except that 500 parts by mass of phenol, 500 parts by mass (solid content) of soda lignin, 136 parts by mass of 47% formalin, and 3.8 parts by mass of oxalic acid were used (see Table 1).

[0067] Synthesis Example 8 A lignin-modified novolac phenolic resin with a modification rate of 25% (hereinafter referred to as "lignin-modified novolac phenolic resin R-8") was obtained under the same conditions and by the same method as in Synthesis Example 1, except that 750 parts by mass of phenol, 250 parts by mass (solid content) of acetic acid lignin, 255 parts by mass of 47% formalin, and 3.8 parts by mass of oxalic acid were used (see Table 1).

[0068] Synthesis Example 9 A lignin-modified novolac phenolic resin with a modification rate of 5% (hereinafter referred to as "lignin-modified novolac phenolic resin R-9") was obtained under the same conditions and by the same method as in Synthesis Example 1, except that 950 parts by mass of phenol, 50 parts by mass (solid content) of acetic acid lignin, 387 parts by mass of 47% formalin, and 3.8 parts by mass of oxalic acid were used (see Table 1).

[0069] Synthesis Example 10 A lignin-modified novolac phenolic resin with a modification rate of 50% (hereinafter referred to as "lignin-modified novolac phenolic resin R-10") was obtained under the same conditions and by the same method as in Synthesis Example 1, except that 500 parts by mass of phenol, 500 parts by mass (solid content) of acetic acid lignin, 136 parts by mass of 47% formalin, and 3.8 parts by mass of oxalic acid were used (see Table 1).

[0070] Synthesis Example 11 A lignin-modified novolac phenolic resin with a modification rate of 25% (hereinafter referred to as "lignin-modified novolac phenolic resin R-11") was obtained under the same conditions and by the same method as in Synthesis Example 1, except that 750 parts by mass of phenol, 50 parts by mass (solid content) of kraft lignin, 200 parts by mass (solid content) of soda lignin, 255 parts by mass of 47% formalin, and 3.8 parts by mass of oxalic acid were used (see Table 1).

[0071] Synthesis Example 12 A lignin-modified novolac phenolic resin with a modification rate of 25% (hereinafter referred to as "lignin-modified novolac phenolic resin R-12") was obtained under the same conditions and by the same method as in Synthesis Example 1, except that 750 parts by mass of phenol, 50 parts by mass (solid content) of kraft lignin, 200 parts by mass (solid content) of acetic acid lignin, 255 parts by mass of 47% formalin, and 3.8 parts by mass of oxalic acid were used (see Table 1).

[0072]

[0073] 2. Production and Evaluation of Resin Compositions for Resin-Coated Sand Using each of the lignin-modified novolac phenolic resins obtained in Synthesis Examples 1 to 12, a lubricant, and a silane coupling agent, resin compositions for resin-coated sand were produced, and the sulfur content was measured.

[0074] Comparative Example 1-1 The lignin-modified novolac phenolic resin R-1 obtained in Synthesis Example 1 was heated to approximately 170°C, and 3 parts by mass of a lubricant (ethylene bisstearic acid amide) and 1 part by mass of a silane coupling agent (3-aminopropyltriethoxysilane) were added to 100 parts by mass of the resin and mixed to obtain a resin composition for resin-coated sand (hereinafter referred to as "resin composition TT-1 for resin-coated sand" or "resin composition TT-1") (see Table 2).

[0075] The sulfur content of the resulting resin composition TT-1 was measured under a helium gas atmosphere using a wavelength dispersive small fluorescent X-ray analyzer "Supermini 200" (trade name) manufactured by Rigaku Corporation, and was found to be 3125 ppm (see Table 2).

[0076] Comparative Examples 1-2 and 1-3 Resin compositions for resin-coated sand (hereinafter referred to as "resin composition TT-2" and "resin composition TT-3") were obtained under the same conditions and by the same method as in Comparative Example 1-1, except that lignin-modified novolac phenolic resins R-2 and R-3 obtained in Synthesis Examples 2 and 3, respectively, were used instead of lignin-modified novolac phenolic resin R-1 (see Table 2).

[0077] Examples 1-1 to 1-9 Resin compositions for resin-coated sand (hereinafter referred to as "resin composition T-1" to "resin composition T-9") were obtained under the same conditions and by the same method as in Comparative Example 1-1, except that lignin-modified novolac phenolic resins R-4 to R-12 obtained in Synthesis Examples 4 to 12 were used instead of lignin-modified novolac phenolic resin R-1 (see Table 2).

[0078] Example 1-10 20 parts by mass of lignin-modified novolac phenolic resin R-1 and 80 parts by mass of lignin-modified novolac phenolic resin R-5 were mixed and heated to approximately 170°C, and 3 parts by mass of a lubricant (ethylene bisstearic acid amide) and 1 part by mass of a silane coupling agent (3-aminopropyltriethoxysilane) were added to the total of 100 parts by mass and mixed to obtain a resin composition for resin-coated sand (hereinafter referred to as "resin composition T-10") (see Table 2).

[0079] Example 1-11 20 parts by mass of lignin-modified novolac phenolic resin R-1 and 80 parts by mass of lignin-modified novolac phenolic resin R-8 were mixed and heated to approximately 170°C, and 3 parts by mass of a lubricant (ethylene bisstearic acid amide) and 1 part by mass of a silane coupling agent (3-aminopropyltriethoxysilane) were added to the resulting mixture (100 parts by mass) and mixed to obtain a resin composition for resin-coated sand (hereinafter referred to as "resin composition T-11") (see Table 2).

[0080]

[0081] 3. Production and Evaluation of Resin-Coated Sand Resin-coated sand was produced using each of the resin compositions for resin-coated sand obtained in Examples 1-1 to 1-11 and Comparative Examples 1-1 to 1-3, Australian natural silica sand "Flattery Sand" (product name, AFS index: 60), a curing agent (hexamethylenetetramine), and a lubricant (calcium stearate).

[0082] Example 2-1: 105 parts by weight of resin composition T-1 for resin-coated sand shown in Table 2 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 sand clumps 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") containing a lignin-modified novolac-type phenolic resin, a lubricant, a curing agent, and a silane coupling agent.

[0083] To conduct a sensory test for sulfur-based gases, 50 grams of the obtained RCS-1 was filled into a mold whose temperature was controlled at 250°C and molded for 60 seconds according to a method in accordance with JIS K 6910 to prepare a JIS test piece (cured molded product, size: 10 mm x 10 mm x 60 mm), and the odor when the mold was opened was evaluated. Five JIS test pieces were prepared and evaluated by the following method (evaluation criteria). <Sensory test method> Sensory evaluation was carried out by 15 odor panelists under conditions of a temperature of 20°C and a relative humidity of 60%, and the obtained sensory evaluation levels were averaged to evaluate. ◎: Almost no sulfur-derived odor is noticeable ○: Sulfur-derived odor is slightly noticeable, but does not interfere with practical use △: Sulfur-derived odor is slightly strong ×: Sulfur-derived odor is very strong

[0084] In the case of RCS-1, the result was "Good" (see Table 3).

[0085] Examples 2-2 to 2-9 and Comparative Examples 2-1 to 2-3 Resin-coated sands were obtained by the same procedure as in Example 2-1, except that resin compositions T-2 to T-9 and TT-1 to TT-3 were used instead of resin composition T-1. The resin-coated sands obtained in Examples 2-2 to 2-9 are referred to as "RCS-2" to "RCS-9." The resin-coated sands obtained in Comparative Examples 2-1 to 2-3 are referred to as "RCS-C1" to "RCS-C3." Subsequently, a sensory test for sulfur-based gases was conducted (see Table 3).

[0086] Example 2-10: Resin-coated sand (hereinafter referred to as "RCS-10") was obtained by the same procedure as in Example 2-1, except that 84 parts by mass of resin composition T-2 and 21 parts by mass of TT-1 were used instead of 105 parts by mass of resin composition T-1. Thereafter, a sensory test for sulfur-based gases was conducted (see Table 3).

[0087] Example 2-11 Resin-coated sand (hereinafter referred to as "RCS-11") was obtained by the same procedure as in Example 2-1, except that 84 parts by mass of resin composition T-5 and 21 parts by mass of TT-1 were used instead of 105 parts by mass of resin composition T-1. Thereafter, a sensory test for sulfur-based gases was conducted (see Table 3).

[0088]

[0089] By using the resin composition for resin-coated sand of the present invention together with aggregate, it is possible to produce resin-coated sand suitable for mold production, which suppresses the emission of unpleasant sulfur-based gases. Furthermore, by subjecting the resin-coated sand of the present invention to, for example, a shell molding method, it is possible to produce a shaped product (such as a mold) that is a hardened molded product of the resin-coated sand under a good working environment. When this shaped product is a mold, it is suitable for producing parts containing metals or alloys used in various industries.

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 which has a sulfur content of 1000 ppm or less.

2. A resin composition for resin-coated sand according to claim 1, wherein the lignin-modified phenolic resin is a reaction product of kraft lignin, a phenol, and an aldehyde.

3. A resin composition for resin-coated sand according to claim 1, wherein the lignin-modified phenolic resin is a reaction product of soda lignin or acetate 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. Resin-coated sand, characterized by comprising the resin composition for resin-coated sand according to any one of claims 1 to 6 and aggregate.

8. Resin-coated sand according to claim 7, wherein at least a portion of the surface of the aggregate is coated with the resin composition for resin-coated sand.

Images