Organic binder for casting mold, and molding sand composition and casting mold obtained using same

Abstract

Provided is an organic binder for a casting mold, which has an excellent hardening rate during the molding of the casting mold, and which enables the obtained casting mold to exhibit excellent strength. The organic binder for a casting mold is configured by using a lignin-modified phenolic resin as a resin binder component and using triethylenediamine. The lignin-modified phenolic resin is preferably a novolac resin modified by at least one of sulfate lignin, diol lignin and acetic acid lignin.

Description

Technical Field

[0001] The present invention relates to an organic binder for a mold, a molding sand composition obtained by using the same, and a mold, and more particularly to an organic binder for a mold, a molding sand composition obtained by using the same, and a mold that can produce a mold having excellent characteristics in a short time. Background Art

[0002] Conventionally, in sand casting represented by shell molding, a shell mold is generally used. Together with refractory particles (molding sand) and a phenolic resin as an adhesive, a hardening agent such as hexamethylenetetramine is further kneaded as needed, and the resulting resin-coated sand (hereinafter, appropriately referred to as "RCS") is heated and formed into a desired shape to obtain a shell mold. Moreover, various adhesives have been proposed and used for RCS used in the manufacture of sand molds such as shell molds and the adhesives used in the manufacture of the RCS.

[0003] On the other hand, in recent years, from the viewpoint of environmental considerations, various studies have been conducted on the use of biomass-derived raw materials corresponding to carbon neutrality for the manufacture of RCS. For example, Patent Document 1 (International Publication No. 2014-136762) proposes a coated sand characterized in that it contains a biomass-derived resin and an aggregate, the biomass-derived resin is a resin containing lignin, and the lignin is lignin obtained by removing cellulose and hemicellulose components from plants by a method using water. In addition, the applicant of the present application is also one of the co-applicants, and Patent Document 2 (Japanese Patent Application Laid-Open No. 2018-118298) proposes a resin-coated sand containing an aggregate and a resin, characterized in that the resin contains a reaction product of lignin, phenols, and aldehydes.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: International Publication No. 2014-136762

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2018-118298 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] Under such circumstances, the present inventors conducted in-depth research on resin-coated sand (RCS) and the resin binder component (adhesive) used therein, and as a result, it was found that, compared with RCS using unmodified phenolic resin, RCS using a phenolic resin modified with lignin (lignin-modified phenolic resin) as the resin binder component has a problem of slow hardening speed during mold shaping. Furthermore, through further in-depth research, it was found that for a molding sand composition (resin-coated sand) obtained by using a substance containing a lignin-modified phenolic resin and triethylenediamine as an organic binder for a mold, the hardening speed during mold shaping is fast, and a mold having strength comparable to that of a conventional RCS using unmodified phenolic resin can be obtained, thus completing the present invention.

[0010] That is, the present invention has been completed against the above background, and the problem to be solved is to provide an organic binder for a mold that has an excellent hardening speed during mold shaping and the mold obtained therefrom exhibits excellent strength. In addition, the problem to be solved by the present invention is also to provide a molding sand composition obtained by using such an organic binder for a mold, and a mold shaped using the molding sand composition.

[0011] Means for Solving the Problem

[0012] Moreover, in order to solve the above-described problems, the present invention can be appropriately implemented in various aspects listed below, and each of the aspects described below can also be adopted in any combination. It should be noted that the aspects or technical features of the present invention are not limited by any of the contents described below, and should be understood as the contents that can be recognized based on the entire description of the specification.

[0013] (1) An organic binder for a mold, characterized by containing a lignin-modified phenolic resin as a resin binder component and containing triethylenediamine.

[0014] (2) The organic binder for a mold according to the above aspect (1), wherein the lignin-modified phenolic resin is a lignin-modified novolac phenolic resin.

[0015] (3) The organic binder for a mold according to the above aspect (1) or the above aspect (2), wherein the lignin-modified phenolic resin is a phenolic resin modified with at least one of sulfate lignin, glycol lignin, and acetic acid lignin.

[0016] (4) The organic binder for a mold according to the above aspect (1) or the above aspect (2), wherein the modification rate of the lignin-modified phenolic resin is 5 to 50%.

[0017] (5) The organic binder for casting molds according to the foregoing scheme (1) or the foregoing scheme (2) further contains aromatic carboxylic acid.

[0018] (6) The organic binder for casting molds according to the foregoing scheme (1) or the foregoing scheme (2), wherein the foregoing triethylenediamine is contained in a proportion of 0.5 to 20 parts by mass relative to 100 parts by mass of the foregoing resin binder component.

[0019] (7) The organic binder for casting molds according to the foregoing scheme (5), wherein the foregoing aromatic carboxylic acid is contained in a proportion of 0.5 to 5 parts by mass relative to 100 parts by mass of the foregoing resin binder component.

[0020] (8) The organic binder for casting molds according to the foregoing scheme (5), wherein the foregoing aromatic carboxylic acid is one or more selected from the group consisting of benzoic acid, salicylic acid, anthranilic acid, and p-aminobenzoic acid.

[0021] (9) A molding sand composition comprising the organic binder for casting molds according to the foregoing scheme (1) or the foregoing scheme (2) and molding sand.

[0022] (10) A casting mold formed by molding and hardening the molding sand composition according to the foregoing scheme (9).

[0023] Effects of the Invention

[0024] Thus, in the organic binder for casting molds of the present invention, since it is composed of a lignin-modified phenolic resin (phenolic resin modified by lignin) as a resin binder component and contains triethylenediamine, when the molding sand composition using such an organic binder for casting molds hardens, triethylenediamine effectively functions as a hardening agent and a hardening accelerator. Therefore, the molding sand composition has an excellent hardening rate during casting mold shaping, and the obtained casting mold exhibits excellent strength. Detailed Embodiments

[0025] However, the organic binder for casting molds of the present invention is composed of a phenolic resin modified by lignin (lignin-modified phenolic resin) as a resin binder component.

[0026] Here, lignin is one of the main components of lignified plant bodies and is a phenolic polymer formed by the enzymatic oxidative polymerization of lignin monomers called monolignols. Monolignols (lignin monomers) are p-hydroxycinnamyl alcohols with a phenylpropane unit (C6-C3 unit) as the basic skeleton, and there are three types: coniferyl alcohol, sinapyl alcohol, and p-coumaryl alcohol. In addition, the aromatic nuclear units of lignin derived from each monolignol are called guaiacyl nuclei (G nuclei), syringyl nuclei (S nuclei), and p-hydroxyphenyl nuclei (H nuclei or P nuclei). However, the detailed structure of lignin is still unclear. Natural lignin is roughly divided into softwood lignin, hardwood lignin, and grass plant lignin (herbaceous lignin). Generally, softwood lignin has G nuclei, hardwood lignin has G nuclei and S nuclei, and grass plant lignin (herbaceous lignin) has G nuclei, S nuclei, and H nuclei. Such natural lignin firmly forms a composite material with polysaccharides (cellulose, hemicellulose) in the cell walls of plants. Therefore, it is very difficult to separate natural lignin without chemical structure modification. Thus, although there are differences in degree, the lignin separated by various methods is called isolated lignin to distinguish it from natural lignin.

[0027] In the present invention, the above-mentioned isolated lignin can be advantageously used in the production of lignin-modified phenolic resins. Examples of such isolated lignin include: a) kraft lignin obtained from the waste liquor of a chemical pulping method called the kraft method, b) lignosulfonate obtained from the waste liquor of a chemical pulping method called the sulfite method, c) sodium lignin (sodium-anthraquinone lignin) derived from an alkaline method (sodium-anthraquinone method) mainly applied to herbaceous plants in chemical pulping, d) organic solvent lignin (such as acetic acid lignin, ethanol lignin, etc.) obtained by the organic solvent method, e) exploded lignin obtained by explosion treatment (high-pressure steam treatment), etc. When producing (preparing) the organic binder for molds of the present invention, phenolic resins modified with kraft lignin, phenolic resins modified with diol lignin (also called modified lignin) separated from cedar (cedar) using polyethylene glycol, and phenolic resins modified with acetic acid lignin are advantageously used. In addition, when producing lignin-modified phenolic resins, of course, only one of the above-mentioned isolated lignins can be used, or two or more lignins can be used.

[0028] Moreover, in the organic binder for casting molds of the present invention, the lignin-modified phenolic resin used as the resin binder component is a solid and / or liquid (e.g., varnish-like or emulsion, etc.) condensation product obtained by reacting lignin, phenols, and aldehydes as described above in the presence of an acidic catalyst or a basic catalyst, and is a resin that exhibits thermosetting by heating in the presence or absence of a specified curing agent and / or curing catalyst. It should be noted that, depending on the catalyst used, a lignin-modified novolak phenolic resin or a lignin-modified resol phenolic resin is formed.

[0029] Here, the phenols used in the production of the lignin-modified phenolic resin refer to phenol and its derivatives. For example, in addition to phenol, alkylphenols such as cresol, xylenol, p-tert-butylphenol, nonylphenol, etc., polyhydric phenols such as resorcinol, bisphenol F, bisphenol A, etc., naphthols, etc., and mixtures thereof, which are well-known substances, can be cited. Moreover, one of them can be used alone or two or more of them can be used in combination.

[0030] In addition, as the aldehydes used in the production of the lignin-modified phenolic resin, for example, in addition to formalin in the form of an aqueous solution of formaldehyde, paraformaldehyde, trioxane, acetaldehyde, paraldehyde, propionaldehyde, etc. can be cited, and furthermore, well-known aldehyde compounds other than these can be appropriately used. Of course, these aldehydes can be used alone or two or more of them can be used in combination.

[0031] The lignin-modified novolak phenolic resin used in the present invention is formed by a condensation reaction using lignin, phenols, and aldehydes, as is well-known, in the presence of an acidic catalyst, such as inorganic acids like hydrochloric acid, sulfuric acid, phosphoric acid, organic acids like oxalic acid, p-toluenesulfonic acid, benzenesulfonic acid, xylenesulfonic acid, and acidic substances like zinc oxide, zinc chloride, magnesium oxide, zinc acetate. It should be noted that at this time, as the mixing molar ratio (F / P) of aldehyde (F) to phenol (P), it can be appropriately selected according to the type of reaction catalyst used, etc., and is preferably selected in the range of 0.30 to 0.85. In addition, in the present invention, in addition to the co-condensation type lignin-modified novolak phenolic resin of lignin and phenols, a modified type lignin-modified novolak phenolic resin obtained by modifying the co-condensation type lignin-modified novolak phenolic resin with a modifier, mixtures thereof, etc. can also be used.

[0032] On the other hand, the lignin-modified resol-type phenolic resin is formed by using lignin, phenols, and aldehydes and performing a condensation reaction using a known basic catalyst in the same manner as in the past. It should be noted that as the basic catalyst, in addition to hydroxides of alkali metals or alkaline earth metals such as sodium hydroxide and calcium hydroxide, and oxides of alkaline earth metals, amines such as dimethylamine, triethylamine, butylamine, dimethylbenzylamine, naphthalenediamine, ammonia, hexamethylenetetramine, naphthenates of other divalent metals, hydroxides of divalent metals, etc. can also be used. In addition, the mixing molar ratio (F / P) of aldehydes and phenols in such a condensation reaction is appropriately selected according to the type of reaction catalyst used, etc., and is usually selected in the range of 1.1 to 4.0. In addition, in the present invention, in addition to the co-condensation type lignin-modified resol-type phenolic resin of lignin and phenols, a modified type lignin-modified resol-type phenolic resin obtained by modifying the co-condensation type lignin-modified resol-type phenolic resin with a modifier, a mixture thereof, etc. can also be used.

[0033] In the present invention, both the above-mentioned lignin-modified novolac-type phenolic resin and lignin-modified resol-type phenolic resin can be used, and the lignin-modified novolac-type phenolic resin is preferably used.

[0034] In addition, when the modification rate (the ratio of lignin to the total amount of lignin and phenols) in the lignin-modified phenolic resin as described above is too low, it may not be possible to advantageously enjoy the effects of the present invention. On the other hand, when it is too high, the hardening speed during mold manufacturing and the strength of the obtained mold may decrease. Therefore, the modification rate in the lignin-modified phenolic resin used in the present invention is preferably 5 to 50%, more preferably 10 to 40%. However, even for a lignin-modified phenolic resin with a high modification rate, by using it in combination with an unmodified phenolic resin, the excellent effects of the present invention can be advantageously enjoyed.

[0035] It should be noted that the organic binder for molds of the present invention takes the above-mentioned lignin-modified phenolic resin as an essential constituent element of the resin binder component. However, in addition to the lignin-modified phenolic resin, as long as the object of the present invention is not hindered, other resins such as unmodified novolac-type phenolic resin and resol-type phenolic resin can also be used in combination.

[0036] Moreover, in the organic binder for molds of the present invention, triethylenediamine is used as an essential constituent element together with the lignin-modified phenolic resin. According to the discovery of the present inventors, triethylenediamine acts advantageously as a hardening agent and a hardening accelerator for the lignin-modified phenolic resin. Therefore, the hardening speed during mold shaping is increased, and the obtained mold exhibits excellent strength.

[0037] If the amount of such triethylenediamine used is too small, it may not be possible to enjoy the effects of the present invention. On the other hand, if the amount used is too large, the finally obtained mold may not exhibit sufficient strength. Therefore, in the present invention, relative to 100 parts by mass of the total amount of the resin component, it is preferably used in a proportion of 0.5 to 20 parts by mass of triethylenediamine.

[0038] In addition, in the present invention, in order to more advantageously exhibit the addition (use) effect of triethylenediamine, it is preferable to use an aromatic carboxylic acid together with triethylenediamine, and its amount used is preferably in a proportion of 0.5 to 5 parts by mass relative to 100 parts by mass of the total amount of the resin component. If the amount of the aromatic carboxylic acid used is too small, it may not be possible to advantageously enjoy its effects. On the other hand, if the amount used is too large, the RCS melting point becomes low, and it may be likely to induce adhesion of the RCS. Examples of the aromatic carboxylic acid that can be used in the present invention include benzoic acid, salicylic acid, anthranilic acid, p-aminobenzoic acid, phthalic acid, isophthalic acid, terephthalic acid, acetylsalicylic acid, o-toluic acid, m-toluic acid, p-toluic acid, o-anisic acid, m-anisic acid, p-anisic acid, o-methylsalicylic acid, m-methylsalicylic acid, p-methylsalicylic acid, gallic acid, trimellitic acid, hydrocinnamic acid, cinnamic acid, methylsalicylic acid, etc. Among them, benzoic acid, salicylic acid, anthranilic acid, and p-aminobenzoic acid can be advantageously used, and benzoic acid can be most advantageously used.

[0039] Moreover, the organic binder for a mold of the present invention formed by the above configuration is compounded in a known molding sand and coats its surface to form a resin-coated sand (RCS) as a molding sand composition for molding a mold such as a shell mold. The amount of the organic binder for a mold used to obtain such an RCS is determined in consideration of the type of the resin binder component contained therein, the required strength of the mold, etc., and therefore cannot be generalized. Usually, it is in the range of about 0.2 to 10 parts by mass relative to 100 parts by mass of the molding sand, preferably 0.5 to 8 parts by mass, and more preferably in the range of 0.5 to 5 parts by mass.

[0040] In addition, regarding the molding sand coated with such an organic binder for casting molds, conventionally well-known molding sands can be appropriately selected, and their types are not particularly limited in the present invention. Such molding sand serves as the base material of the casting mold. Therefore, as long as it is an inorganic refractory particle having a fire resistance capable of withstanding casting and a particle size suitable for mold formation (molding), conventionally well-known inorganic particles that have been used in shell mold casting can be used. In addition, as such refractory particles, for example, in addition to silica sand that is commonly used, special sands such as olivine sand, zircon sand, chromite sand, and alumina sand, slag-based particles such as ferrochrome slag, nickel-iron slag, and converter slag, mullite-based artificial particles such as Naigai Cerabeads (trade name, manufactured by ITOCHUCERATECH CORP.), or recycled particles obtained by recycling and regenerating them after casting can be mentioned. They can be used alone or in combination of two or more kinds.

[0041] It should be noted that when manufacturing RCS as the molding sand composition of the present invention, lubricants that contribute to improving the fluidity of RCS and the like can be used. Among such lubricants, for example, waxes such as paraffin, synthetic polyethylene wax, and montanic acid wax can be used (compounded) both during the manufacture of lignin-modified phenolic resin and during the manufacture of RCS; 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, etc. In addition, stearic acid, stearyl alcohol, lead stearate, zinc stearate, calcium stearate, magnesium stearate, monoglyceryl stearate, stearyl stearate, hydrogenated oil, etc., which function as lubricants, can be used (compounded) during the manufacture of RCS. On the other hand, it is also effective to use a coupling agent that strengthens the bond between the refractory aggregate and the lignin-modified phenolic resin. For example, coupling agents such as silane coupling agents, zircon coupling agents, and titanium coupling agents can be used (compounded) both during the manufacture of lignin-modified phenolic resin and during the manufacture of RCS. Furthermore, as a mold release agent, paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, graphite microparticles, mica, vermiculite, fluorine-based mold release agents, silicone-based mold release agents, etc. can also be used (compounded).

[0042] In addition, when manufacturing the target RCS using the organic binder for casting molds of the present invention, the manufacturing method is not particularly limited, and conventionally known methods such as dry heat coating method, semi-heat coating method, cold coating method, powder solvent method, etc. can all be adopted. In the present invention, the so-called dry heat coating method described below is particularly recommended: in a muller such as a swing mixer or a high-speed mixer, after preheating the molding sand and kneading the resin binder component constituting the organic binder for casting molds, an aqueous solution of a hardening accelerator is added as needed, and the lumpy content is disintegrated into granular form by blowing air for cooling, and calcium stearate (lubricating material) is added. In addition, the timing of kneading the organic binder for casting molds of the present invention with the molding sand can be appropriately selected.

[0043] Furthermore, when molding a specified mold such as a shell mold using the RCS obtained as described above, in order to achieve the heat hardening of the RCS, the molding of the target mold is carried out under heating. As such a heating molding method, there is no particular limitation, and conventionally known methods can all be advantageously used. For example, the above-mentioned RCS is filled into a molding die heated to 150°C to 300°C having a space providing the desired shape of the target mold by means of gravity dropping method, blowing method, etc., and after hardening, the hardened mold is demolded from the molding die, thereby a casting mold can be obtained. Moreover, in the mold thus obtained, the excellent characteristics as described above can be advantageously imparted.

[0044] Examples

[0045] Hereinafter, several examples of the present invention are shown to more specifically illustrate the present invention. However, the present invention is of course not limited by any of the descriptions of such examples. In addition, it should be understood that in the present invention, in addition to the following examples and further in addition to the above specific descriptions, various changes, corrections, improvements, etc. can be made based on the knowledge of those skilled in the art as long as the gist of the present invention is not deviated from.

[0046] It should be noted that the respective characteristics of the RCS manufactured below are measured according to the following test methods. For the measured values of each RCS based on each test, in order to compare with the measured values of the RCS obtained using the organic binder for casting molds of Comparative Example 1 (an organic binder for casting molds composed only of unmodified linear phenolic resin), the measured values of the RCS of Comparative Example 1 are used as reference values. More specifically, for the flexural strength and RCS fusion points, the measured values of the RCS of Comparative Example 1 are set to 100, and for the flexural amount, the measured values of the RCS of Comparative Example 1 are set to 300, and the values calculated respectively are recorded as evaluations in Table 1 - Table 2 below.

[0047] - Example 1 -

[0048] 750 parts by mass of phenol, 385 parts by mass of sulfate lignin (manufactured by UPM-Kymmene Oyj, purity: 65%), 244 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 stirring device, and a condenser. It should be noted that the mixing molar ratio (F / P) of phenol to formalin was 0.48. Then, the reaction vessel was slowly heated until it reached the reflux temperature, and a reflux reaction was carried out for 180 minutes. Further heating and concentration under reduced pressure were carried out until the temperature of the reaction solution reached 190 °C, thereby obtaining a lignin-modified linear phenolic resin (resin a) with a modification rate of 25%. Immediately after concentration under reduced pressure, it was slowly cooled to about 170 °C. In the resin a, triethylenediamine was added in a proportion of 5 parts by mass relative to 100 parts by mass of resin a and mixed, thereby obtaining an organic binder for casting (Example 1).

[0049] - Examples 2 to 5 -

[0050] The mixing ratio of triethylenediamine relative to 100 parts by mass of resin a was changed to 0.5 part by mass, 2 parts by mass, 10 parts by mass, and 20 parts by mass as shown in Table 1 below. Except for this, the organic binder for casting (Examples 2 to 5) was obtained according to the same conditions and methods as in Example 1.

[0051] - Examples 6 to 8 -

[0052] As shown in Table 1 below, benzoic acid was added and mixed with triethylenediamine in a proportion of 2 parts by mass, 0.5 part by mass, or 5 parts by mass relative to 100 parts by mass of resin a. Except for this, the organic binder for casting (Examples 6 to 8) was obtained according to the same conditions and methods as in Example 1.

[0053] - Examples 9 to 11 -

[0054] As shown in Table 1 below, any one of salicylic acid, anthranilic acid, or p-aminobenzoic acid was added and mixed with triethylenediamine in a proportion of 2 parts by mass relative to 100 parts by mass of resin a. Except for this, the organic binder for casting (Examples 9 to 11) was obtained according to the same conditions and methods as in Example 1.

[0055] - Example 12 -

[0056] Into a reaction vessel equipped with a thermometer, a stirring device, and a condenser, 950 parts by mass of phenol, 77 parts by mass of sulfate lignin, 387 parts by mass of 47% formalin, and 4.8 parts by mass of oxalic acid were charged. It should be noted that the mixing molar ratio (F / P) of phenol to formalin is 0.60. Then, the reaction vessel was slowly heated until it reached the reflux temperature, and a reflux reaction was carried out for 180 minutes. Further heating and concentration under reduced pressure were carried out until the temperature of the reaction solution reached 190 °C, whereby a lignin-modified linear phenolic resin (resin b) with a modification rate of 5% was obtained. Immediately after concentration under reduced pressure, it was slowly cooled to about 170 °C to obtain resin b, and triethylenediamine was added in a proportion of 5 parts by mass relative to 100 parts by mass of resin b and mixed, whereby an organic binder for casting (Example 12) was obtained.

[0057] - Example 13 -

[0058] Except for using 500 parts by mass of phenol, 769 parts by mass of sulfate lignin, and 136 parts by mass of 47% formalin, according to the same conditions and methods as in Example 12, after obtaining a lignin-modified linear phenolic resin (resin c) with a modification rate of 50%, an organic binder for casting (Example 13) was obtained.

[0059] - Example 14 -

[0060] Except for using 400 parts by mass of phenol, 923 parts by mass of sulfate lignin, and 95 parts by mass of 47% formalin, according to the same conditions and methods as in Example 12, after obtaining a lignin-modified linear phenolic resin (resin d) with a modification rate of 60%, an organic binder for casting (Example 14) was obtained.

[0061] - Example 15 -

[0062] Except for using 253 parts by mass of glycol lignin (manufactured by LignoMateria, purity: 99%) instead of sulfate lignin, according to the same conditions and methods as in Example 1, after obtaining a lignin-modified linear phenolic resin (resin e) with a modification rate of 25%, an organic binder for casting (Example 15) was obtained.

[0063] - Example 16 -

[0064] Except for using 269 parts by mass of acetic acid lignin (purity: 93%) instead of sulfate lignin, according to the same conditions and methods as in Example 1, after obtaining a lignin-modified linear phenolic resin (resin f) with a modification rate of 25%, an organic binder for casting (Example 16) was obtained.

[0065] - Example 17 -

[0066] First, 1000 parts by mass of phenol, 441 parts by mass of 47% formalin, and 5 parts by mass of oxalic acid are charged into a reaction vessel equipped with a thermometer, a stirring device, and a condenser. It should be noted that the mixing molar ratio of phenol to formalin (F / P) is 0.65. Then, the reaction vessel is slowly heated until it reaches the reflux temperature, and a reflux reaction is carried out for 180 minutes. Further heating and vacuum concentration are carried out until the temperature of the reaction solution reaches 190 °C, thereby obtaining a linear phenolic resin (resin g).

[0067] To a mixture of 50 parts by mass of resin g that has been slowly cooled immediately after vacuum concentration to approximately 170 °C and 50 parts by mass of resin c that has also been slowly cooled immediately after vacuum concentration to approximately 170 °C, triethylenediamine is added in a proportion of 5 parts by mass relative to 100 parts by mass of the mixture and mixed, thereby obtaining an organic binder for casting (Example 17).

[0068] - Comparative Example 1 -

[0069] Only resin a (lignin-modified linear phenolic resin with a modification rate of 25%) is used as a binder for casting (Comparative Example 1).

[0070] - Comparative Example 2 -

[0071] Only sulfate lignin is used as a binder for casting (Comparative Example 2).

[0072] - Manufacture of RCS Using an Organic Binder for Casting -

[0073] 7000 parts of Flattery silica sand heated to 145 °C are put into a pan muller, and 105 parts by mass of the above-obtained organic binder for casting are further added. Mixing is carried out until the sand grains disintegrate, and then after air cooling, 7 parts of calcium stearate are further added to obtain a shell mold RCS using each organic binder for casting. It should be noted that an attempt was made to manufacture an RCS using the organic binder for casting composed only of sulfate lignin in Comparative Example 2, but mixing was not possible and an RCS could not be obtained. Therefore, in Table 2 below, "unable to mold" is recorded in the evaluation column of Comparative Example 2.

[0074] - Measurement of Flexural Strength -

[0075] Using each RCS obtained as described above, JIS type test pieces (10 mm × 10 mm × 60 mm, firing conditions: 250 °C × 60 seconds) are fabricated in accordance with JIS-K-6910. For the obtained JIS type test pieces, the flexural strength (kgf / cm 2 ) is measured in accordance with the JACT test method: SM-1. The larger the value shown in Table 1 - Table 2 below, the higher the strength of the mold.

[0076] -Measurement of bending (300 gf) amount

[0077] According to the JACT test method: the flexure test method of SM-3, for each test piece (180 mm × 40 mm × 5 mm, firing conditions: 250 °C × 40 s) obtained using each RCS, a load of 300 gf is applied to the central part thereof, and the strain amount (mm) at the central part of the test piece after 3 minutes of placement is read with a micrometer, and this value is taken as the bending (300 gf) amount. This bending amount (flexure amount) is a standard index indicating the workability after just performing mold casting and the mold hardening speed. The smaller the values shown in Table 1 - Table 2 below, the faster the mold hardening speed and the better the workability.

[0078] -Measurement of RCS weld point

[0079] For the welding temperature of each RCS, it is measured according to the JACT test method: C-1 (weld point test method). The larger the values shown in Table 1 to Table 2 below, the more excellent the anti-adhesion property of the RCS.

[0080] [Table 1]

[0081]

[0082] [Table 2]

[0083]

[0084] It can be clearly seen from the results of Table 1 - Table 2 that when the RCS is obtained using the organic binder for mold of the present invention, the mold obtained therefrom has a smaller value of the bending amount compared with the mold formed by the RCS using the organic binder for mold (Comparative Example 1) containing only lignin-modified linear phenolic resin (resin a). Therefore, the mold hardening speed is fast, and excellent strength equal to or higher than that is exhibited.

Claims

1. An organic binder for a mold, characterized in that, It contains a lignin-modified phenolic resin as a resin binder component and contains triethylenediamine.

2. The organic binder for a mold according to claim 1, wherein, The lignin-modified phenolic resin is a lignin-modified linear phenolic resin.

3. The organic binder for a mold according to claim 1 or 2, wherein, The lignin-modified phenolic resin is a phenolic resin modified by at least one of sulfate lignin, glycol lignin, and acetic acid lignin.

4. The organic binder for a mold according to claim 1 or 2, wherein, The modification rate of the lignin-modified phenolic resin is 5 to 50%.

5. The organic binder for casting according to claim 1 or 2, further comprising an aromatic carboxylic acid.

6. The organic binder for a mold according to claim 1 or 2, wherein, The triethylenediamine is contained in a proportion of 0.5 to 20 parts by mass relative to 100 parts by mass of the resin binder component.

7. The organic binder for a mold according to claim 5, wherein, The aromatic carboxylic acid is contained in a proportion of 0.5 to 5 parts by mass relative to 100 parts by mass of the resin binder component.

8. The organic binder for a mold according to claim 5, wherein, The aromatic carboxylic acid is one or more selected from the group consisting of benzoic acid, salicylic acid, anthranilic acid, and p-aminobenzoic acid.

9. A molding sand composition comprising the organic binder for casting according to claim 1 or 2 and molding sand.

10. A casting mold formed by molding and hardening the molding sand composition according to claim 9.

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