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

Abstract

Provided is an organic binder for casting molds, which has an excellent hardening rate during the molding of a casting mold, and which gives a casting mold that exhibits excellent strength. The organic binder for a casting mold is configured by using triethylenediamine together with one or more resins selected from the group consisting of cresol-modified novolac resins, novolac resin-type cresol resins, xylenol-modified novolac resins, and novolac resin-type xylenol resins as resin binder components.

Description

Technical Field

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

[0002] In sand casting represented by shell casting, a shell casting mold is usually used, which is obtained by kneading refractory particles (molding sand) and a phenolic resin as a binder and a hardener such as hexamethylenetetramine as needed to obtain resin coated sand (hereinafter, appropriately referred to as "RCS"), and using the obtained resin coated sand, it is heated and molded into a desired shape. In addition, various RCS used in the manufacture of sand molds such as shell casting molds and binders used in the manufacture of the above RCS have been proposed and used.

[0003] For example, Patent Document 1 (Japanese Patent Laid-Open No. 1-135814) proposes a phenolic resin for shell molds that generates less odor during shell mold molding, which is obtained by reacting phenols and formaldehydes using an acidic substance as a catalyst, and is characterized in that the content of mononuclear components in the phenolic resin is less than 1% by weight, and the content of binuclear components is less than 2% by weight. In addition, Patent Document 2 (Japanese Patent Laid-Open No. 2003-170244) proposes a resin-coated sand for shell molds that has hardenability and excellent moldability even when hexamine, which is a hardener, is reduced, and is obtained by kneading a refractory granular material, an alkali metal weak acid salt or an alkali metal hydroxide, a phenolic resin, and hexamethylenetetramine.

[0004] Furthermore, Patent Document 3 (Japanese Patent Publication No. 58-119433) proposes a resin-coated sand for preventing cracks generated when pouring into a mold, which is formed by covering polyethylene glycol present in a refractory granular material for a mold with a phenolic resin. Furthermore, Patent Document 4 (Japanese Patent Publication No. 4369653) proposes a resin-coated sand for a mold, which is capable of further shortening the manufacturing time of a mold, characterized in that the surface of a refractory aggregate is covered with a phenolic resin binder and a reactive hardening accelerator, wherein the phenolic resin binder is formed of a resol-type phenolic resin and a linear phenolic resin in a predetermined ratio (mass ratio), and an amine compound selected from melamine, urea, and dicyandiamide is used as a reactive hardening accelerator.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 1-135814

[0008] Patent Document 2: Japanese Patent Application Publication No. 2003-170244

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 58-119433

[0010] Patent Document 4: Japanese Patent No. 4369653 Summary of the invention

[0011] Problem that the invention aims to solve

[0012] Under such circumstances, the present inventors have conducted intensive research on resin-coated sand and resin bonding components (binders) used therefor, and have determined that, although the strength of the final mold obtained by using modified novolac resins or the like as the resin bonding component is improved compared to the case of using unmodified phenolic resins as the resin bonding component, there is a problem that the curing speed of the mold itself is slow. Then, further intensive research has been conducted, and as a result, it has been found that, when a specific resin such as cresol-modified novolac resin and triethylenediamine are used as an organic binder for molds, the obtained molding sand composition (resin-coated sand) has a fast curing speed during mold molding, and also a mold exhibiting excellent strength can be obtained, and the present invention has been completed.

[0013] That is, the present invention is made against the background of the above situation, and the problem to be solved is to provide an organic binder for a mold that has an excellent hardening speed during mold molding and the obtained mold exhibits excellent strength. In addition, the problem to be solved by the present invention is to provide a molding sand composition obtained by using such an organic binder for a mold, and a casting mold molded by using the above molding sand composition.

[0014] Solutions for solving problems

[0015] Moreover, in order to solve such a problem, the present invention can be appropriately implemented in various schemes as listed below, and each scheme described below can also be adopted in any combination. It should be noted that the scheme to technical features of the present invention are not limited by the following description, and should be understood to be understood based on the description of the entire specification.

[0016] (1) An organic binder for a casting mold, characterized in that it contains one or more resins selected from the group consisting of cresol-modified novolac resins, novolac-type cresol resins, xylenol-modified novolac resins and novolac-type xylenol resins as resin binder components, and contains triethylenediamine.

[0017] (2) The organic binder for a casting mold according to the above-mentioned embodiment (1), further comprising an aromatic carboxylic acid.

[0018] (3) The organic binder for a casting mold according to the above aspect (1) or (2), wherein the triethylenediamine is contained in a ratio of 0.5 to 20 parts by mass based on 100 parts by mass of the resin binder component.

[0019] (4) The organic binder for a casting mold according to the above aspect (2), wherein the aromatic carboxylic acid is contained in a ratio of 0.5 to 5 parts by mass based on 100 parts by mass of the resin binder component.

[0020] (5) The organic binder for a casting mold according to the above embodiment (2), 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.

[0021] (6) A molding sand composition comprising the organic binder for a mold according to the above-mentioned aspect (1) or (2) and molding sand.

[0022] (7) A casting mold, which is obtained by molding and hardening the molding sand composition described in the above-mentioned embodiment (6).

[0023] Effects of the Invention

[0024] Thus, the organic binder for a mold according to the present invention comprises one or more resins selected from the group consisting of cresol-modified novolac resin, novolac-type cresol resin, xylenol-modified novolac resin and novolac-type xylenol resin as resin binder components, and is composed of triethylenediamine. Thus, when the molding sand composition formed by using such an organic binder for a mold is hardened, triethylenediamine functions efficiently as a hardener and hardening accelerator. Thus, the molding sand composition has an excellent hardening speed during mold forming, and the obtained mold has excellent strength. Specific implementation plan

[0025] Thus, the organic binder for a casting mold according to the present invention contains one or more resins selected from the group consisting of cresol-modified novolac resins, novolac-type cresol resins, xylenol-modified novolac resins and novolac-type xylenol resins as a resin binder component.

[0026] For such a specific resin, first, as a cresol-modified novolac resin, for example, there can be exemplified: a co-condensation type cresol-modified novolac resin of cresol and phenol obtained by reacting cresol and phenol with aldehydes in the presence of an acidic catalyst or the like; a modified cresol-modified novolac resin obtained by modifying the above-mentioned co-condensation type cresol-modified novolac resin with a modifier (modifier); and mixtures thereof, etc.

[0027] If the modification rate (the ratio of cresol to the total amount of cresol and phenol) in the cresol-modified novolac resin is too low, there is a concern that the effect of the present invention cannot be advantageously enjoyed. On the other hand, if it is too high, there is a concern that the hardening speed during mold manufacturing is reduced. Therefore, the modification rate in the cresol-modified novolac resin used in the present invention is preferably 5 to 70%, more preferably 5 to 50%, and most preferably 10 to 40%. In particular, even a cresol-modified novolac resin with a high modification rate can be advantageously used with an unmodified novolac resin to enjoy the excellent effect of the present invention. It should be noted that the following methods can be used in conjunction with a cresol-modified novolac resin: a method in which these resins are synthesized (manufactured) separately and then melt-mixed; a method in which these resins are simultaneously added and kneaded when manufacturing RCS; etc., and they can be used in conjunction at any time as long as the purpose of the present invention is not hindered.

[0028] In addition, the novolac type cresol resin refers to a resin obtained by reacting cresol with aldehydes in the presence of an acidic catalyst or the like. In the case of using the novolac type cresol resin in the present invention, if the amount thereof (the proportion in the resin binder component) is too much, there is a concern that the effect of the present invention cannot be enjoyed advantageously, and therefore, the novolac type cresol resin is preferably used in combination with a novolac resin. It should be noted that regarding the use of the novolac type cresol resin and the novolac resin in combination, the following methods can be exemplified: a method of synthesizing (manufacturing) these resins separately and then melt-mixing them; a method of simultaneously adding these resins and kneading them when manufacturing RCS; etc., as long as the purpose of the present invention is not hindered, they can be used in combination at any time.

[0029] It should be noted that it is known that there are three structural isomers (o-cresol, m-cresol, and p-cresol) in cresol. As a result, the cresol-modified novolac resin used in the present invention can be modified from any structural isomer, and similarly, the novolac-type cresol resin used in the present invention can be synthesized (produced) using any structural isomer.

[0030] On the other hand, examples of the xylenol-modified phenolic resin include: a co-condensation type xylenol-modified phenolic resin of xylenol and phenol obtained by reacting xylenol, phenol and aldehydes in the presence of an acidic catalyst or the like; a modified xylenol-modified phenolic resin obtained by modifying the co-condensation type xylenol-modified phenolic resin with a modifier (modifier); and mixtures thereof.

[0031] If the modification rate (ratio of xylenol to the total amount of xylenol and phenol) in the above-mentioned xylenol-modified novolac resin is too low, there is a concern that the effect of the present invention cannot be advantageously enjoyed. On the other hand, if it is too high, there is a concern that the curing speed during mold manufacturing is reduced. Therefore, the modification rate in the xylenol-modified novolac resin used in the present invention is preferably 5 to 70%, more preferably 5 to 50%, and most preferably 10 to 40%. In particular, even a xylenol-modified novolac resin with a high modification rate can be advantageously used with an unmodified novolac resin to enjoy the excellent effect of the present invention. It should be noted that the following methods can be used in conjunction with a xylenol-modified novolac resin: a method of synthesizing (manufacturing) these resins separately and then melt-mixing them; a method of simultaneously adding these resins and kneading them when manufacturing RCS, etc., as long as the purpose of the present invention is not hindered, they can be used in conjunction at any time.

[0032] In addition, the novolac type xylenol resin refers to a product obtained by reacting xylenol with aldehydes in the presence of an acidic catalyst or the like. In the case of using the novolac type xylenol resin in the present invention, if the amount (the proportion in the resin binder component) of the novolac type xylenol resin is too much, there is a concern that the effect of the present invention cannot be enjoyed to its full potential. Therefore, the novolac type xylenol resin is preferably used in combination with a novolac resin. It should be noted that regarding the use of the novolac type xylenol resin and the novolac resin in combination, the following methods can be exemplified: a method of synthesizing (manufacturing) these resins separately and then melt-mixing them; a method of simultaneously adding these resins and kneading them when manufacturing RCS, etc. As long as the purpose of the present invention is not hindered, they can be used in combination at any time.

[0033] It should be noted that it is known that there are 6 structural isomers of xylenol (2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol). As a result, the xylenol-modified novolac resin used in the present invention can be modified from any structural isomer, and similarly, the novolac-type xylenol resin used in the present invention can be synthesized (produced) using any structural isomer.

[0034] The present invention uses the above-mentioned specific resin as an essential constituent element in the form of a resin binder component. However, in addition to the above-mentioned specific resin, other resins may be used in combination as long as the purpose of the present invention is not impaired.

[0035] Furthermore, the organic binder for a casting mold according to the present invention comprises triethylenediamine as an essential constituent element together with a specific resin represented by a cresol-modified novolac resin. According to the knowledge of the present inventors, triethylenediamine advantageously functions as a curing agent and a curing accelerator for the specific resin, thereby improving the curing speed during the molding of the casting mold and exhibiting excellent strength in the obtained casting mold.

[0036] If the amount of triethylenediamine used is too small, the effect of the present invention may not be achieved, while if the amount is too large, the final mold may not have sufficient strength. Therefore, in the present invention, triethylenediamine is preferably used in a ratio of 0.5 to 20 parts by mass relative to 100 parts by mass of the total amount of the resin component.

[0037] In addition, in the present invention, in order to more advantageously demonstrate the effect of adding (using) triethylenediamine, it is preferred to use an aromatic carboxylic acid together with triethylenediamine, and the amount used is preferably 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, there is a concern that the effect cannot be advantageously enjoyed, while on the other hand, if the amount used is too large, the RCS melting point becomes low, and there is a concern that it becomes easy to induce RCS adhesion. 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, and the like. Among these, benzoic acid, salicylic acid, anthranilic acid, and p-aminobenzoic acid are advantageously used, and benzoic acid is most advantageously used.

[0038] The organic binder for molds according to the present invention thus constituted is mixed with known molding sand to cover the surface thereof, thereby forming an RCS as a molding sand composition for molding a mold such as a shell mold. The amount of the organic binder for molds used to obtain such an RCS is determined in consideration of the type of resin bonding component contained therein, the required strength of the mold, etc., and therefore cannot be generally limited, but is generally within the range of about 0.2 to 10 parts by mass, preferably 0.5 to 8 parts by mass, and more preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of the molding sand.

[0039] In addition, about the molding sand covered by such mold organic binder, it is suitable to select and can use known all the time, and its kind is not particularly limited for the present invention.Such molding sand is used to form the base material of mold, therefore, as long as it is inorganic refractory particles with the refractory property that can withstand casting and the particle diameter that is suitable for mold formation (molding), it is possible to use the known inorganic particles used in shell casting all the time.In addition, as such refractory particles, for example, except the silica sand that is usually often used, it is also possible to enumerate: slag particles such as olivine sand, zircon sand, chrome sand, special sands such as alumina sand, ferrochrome alloy slag, ferronickel alloy slag, converter slag, Naigai Cerabeads (trade name: ITOCHU CERATECH CORP. system) such mullite artificial particles or the regenerated particles obtained after they are cast through recovery / regeneration, etc., they can be used alone or combined with more than 2 kinds and used.

[0040] It should be noted that when the target RCS is manufactured using the organic binder for molds according to the present invention, there is no particular limitation on the manufacturing method thereof, and any of the methods known to the public, such as dry hot coating method, semi-hot coating method, cold coating method, powder solvent method, etc., can be used. For the present invention, the so-called dry hot coating method as follows is particularly recommended: in a mixer such as a pendulum sand mixer or a high-speed sand mixer, the preheated molding sand is mixed with the resin bonding component constituting the organic binder for molds, and an aqueous solution of a hardening accelerator is added as needed, and the block contents are disintegrated into granules by air cooling, and calcium stearate (lubricating material) is added. In addition, the time for mixing the organic binder for molds according to the present invention with the molding sand can be appropriately selected.

[0041] Furthermore, when the RCS obtained as described above is used to shape a predetermined mold such as a shell mold, in order to achieve heat hardening of the above RCS, the target mold is shaped under heating. There is no particular limitation as to such a heating shaping method, and any method that has been known can be advantageously used. For example, by using a gravity drop method, a blowing method, etc., the RCS as described above is filled into a molding mold that has a desired shape space for providing the target mold and is heated to 150°C to 300°C and hardened, and then the hardened mold is demolded from the above molding mold to obtain a casting mold. Moreover, the mold obtained in this way is advantageously endowed with the excellent characteristics described above. Specific embodiments

[0043] Hereinafter, several embodiments of the present invention are shown to further specifically illustrate the present invention, but the present invention is certainly not subject to any limitation of the description of such embodiments. In addition, it should be understood that in the present invention, in addition to the following embodiments and in addition to the above-mentioned specific description, various changes, modifications, improvements, etc. can be applied based on the common sense of those skilled in the art as long as they do not depart from the gist of the present invention.

[0044] It should be noted that the various properties of the RCS manufactured below were measured according to the following test method. For the measured values ​​of each RCS based on each test, in order to compare with the measured values ​​of RCS obtained using the organic binder for castings of Comparative Example 1 (the organic binder for castings formed only by unmodified linear phenolic resin), the measured value of RCS of Comparative Example 1 was calculated as a reference value (100), and it was recorded as an evaluation in the following Tables 1 to 3.

[0045] -Example 1-

[0046] In the reaction vessel equipped with thermometer, stirring device and condenser, phenol 658 mass parts, o-cresol 282 mass parts, 47% formalin 399 mass parts and oxalic acid 4.7 mass parts are put into.It should be noted that the mixing molar ratio (F / P class) of phenols (phenol and o-cresol) and formalin is 0.65.Then, the reaction vessel is slowly heated up, and after reaching reflux temperature, reflux reaction is carried out for 240 minutes, and further heating and reduced pressure concentration are carried out until the reaction liquid temperature becomes 190 ℃, thereby obtaining the o-cresol modified linear phenolic resin (resin a) with a modification rate of 30%.In the resin a that is slowly cooled to about 170 ℃ after just reduced pressure concentration, triethylenediamine is added and mixed in a ratio of 5 mass parts relative to 100 mass parts of resin a, thereby obtaining an organic binder for casting (Example 1).

[0047] -Example 2 to Example 5-

[0048] As shown in Table 1 below, organic binders for casting molds (Examples 2 to 5) were obtained under the same conditions and method as in Example 1, except that the blending ratio of triethylenediamine relative to 100 parts by mass of resin a was changed to 0.5 parts by mass, 2 parts by mass, 10 parts by mass, and 20 parts by mass.

[0049] -Example 6 to Example 8-

[0050] As shown in Table 1 below, organic binders for casting molds (Examples 6 to 8) were obtained under the same conditions and method as in Example 1, except that benzoic acid was added and mixed together with triethylenediamine in a ratio of 2 parts by mass, 0.5 parts by mass or 5 parts by mass relative to 100 parts by mass of resin a.

[0051] -Example 9 to Example 11-

[0052] As shown in Table 1 below, salicylic acid, o-aminobenzoic acid or p-aminobenzoic acid was added and mixed together with triethylenediamine in a ratio of 2 parts by mass relative to 100 parts by mass of resin a, and except that the same conditions and method as in Example 1 were followed to obtain an organic binder for a casting mold (Examples 9 to 11).

[0053] -Example 12-

[0054] In a reaction vessel equipped with a thermometer, a stirring device and a condenser, phenol 893 mass parts, o-cresol 47 mass parts, 47% formalin 412 mass parts and oxalic acid 4.7 mass parts are added. It should be noted that the mixing molar ratio (F / P class) of phenols (phenol and o-cresol) and formalin is 0.65. Then, the reaction vessel is slowly heated up, and after reaching the reflux temperature, a reflux reaction is carried out for 240 minutes, and further heating and reduced pressure concentration are carried out until the reaction liquid temperature becomes 190°C, thereby obtaining an o-cresol modified linear phenolic resin (resin b) with a modification rate of 5%. In the resin b that has been slowly cooled to about 170°C after just reduced pressure concentration, triethylenediamine is added and mixed in a ratio of 5 mass parts relative to 100 mass parts of resin b, thereby obtaining an organic binder for casting (Example 12).

[0055] -Example 13-

[0056] Using 799 parts by mass of phenol, 141 parts by mass of o-cresol and 407 parts by mass of 47% formalin, the same conditions and methods as in Example 12 were used to obtain an o-cresol-modified linear phenolic resin (resin c) having a modification rate of 15%, and then an organic binder for casting was obtained (Example 13).

[0057] -Example 14-

[0058] Using 470 parts by mass of phenol, 470 parts by mass of o-cresol and 388 parts by mass of 47% formalin, the same conditions and methods as in Example 12 were followed to obtain an o-cresol-modified linear phenolic resin (resin d) having a modification ratio of 50%, and then an organic binder for casting was obtained (Example 14).

[0059] -Example 15-

[0060] Using 282 parts by mass of phenol, 658 parts by mass of o-cresol and 377 parts by mass of 47% formalin, the same conditions and methods as in Example 12 were used to obtain an o-cresol-modified linear phenolic resin (resin e) with a modification rate of 50%, and then an organic binder for casting was obtained (Example 15).

[0061] -Example 16-

[0062] Except for using m-cresol instead of o-cresol, the same conditions and method as in Example 1 were followed to obtain a m-cresol-modified novolac resin (resin g) having a modification rate of 30%, thereby obtaining an organic binder for a mold (Example 16).

[0063] -Example 17-

[0064] A p-cresol-modified novolac resin (resin h) having a modification rate of 30% was obtained under the same conditions and method as in Example 1 except that p-cresol was used instead of o-cresol, thereby obtaining an organic binder for a mold (Example 17).

[0065] -Example 18-

[0066] Except that 141 parts by mass of m-cresol and 141 parts by mass of p-cresol were used instead of 282 parts by mass of o-cresol, the same conditions and method as in Example 1 were followed to obtain a m- / p-cresol-modified linear phenolic resin (resin i) having a modification ratio of 30%, and then an organic binder for casting was obtained (Example 18).

[0067] -Example 19-

[0068] Except that 169 parts by mass of m-cresol and 113 parts by mass of p-cresol were used instead of 282 parts by mass of o-cresol, the same conditions and method as in Example 1 were followed to obtain a m- / p-cresol-modified linear phenolic resin (resin j) having a modification ratio of 30%, and then an organic binder for casting was obtained (Example 19).

[0069] -Example 20-

[0070] Using 2,5-xylenol instead of o-cresol and using 386 parts by mass of 47% formalin, the same conditions and method as in Example 1 were followed to obtain a 2,5-xylenol-modified linear phenolic resin (resin k) having a modification rate of 30%, thereby obtaining an organic binder for a casting mold (Example 20).

[0071] -Example 21-

[0072] 3,5-Xylenol was used instead of o-cresol. In addition, 386 parts by mass of 47% formalin was used. The same conditions and methods as in Example 1 were followed to obtain a 3,5-Xylenol-modified linear phenolic resin (Resin 1) having a modification rate of 30%, and then an organic binder for a casting mold was obtained (Example 21).

[0073] -Example 22-

[0074] 3,4-xylenol was used instead of o-cresol. In addition, 386 parts by mass of 47% formalin was used. The same conditions and methods as in Example 1 were followed to obtain a 3,4-xylenol-modified linear phenolic resin (resin m) having a modification rate of 30%, thereby obtaining an organic binder for a casting mold (Example 22).

[0075] -Example 23-

[0076] First, in a reaction vessel equipped with a thermometer, a stirring device and a condenser, 940 parts by mass of o-cresol, 361 parts by mass of 47% formalin and 4.7 parts by mass of oxalic acid are added. It should be noted that the molar ratio of o-cresol to formalin (F / P type) is 0.65. Then, the reaction vessel is slowly heated to reach the reflux temperature, and then reflux reaction is carried out for 240 minutes, and further heating and reduced pressure concentration are carried out until the reaction liquid temperature becomes 190°C, thereby obtaining a linear phenolic resin type cresol resin (resin f). On the other hand, phenol is used instead of o-cresol, and 415 parts by mass of 47% formalin are used. In addition, according to the same conditions and methods, a linear phenolic resin (resin n) is obtained.

[0077] To a mixture of 30 parts by mass of resin f which had been slowly cooled to about 170°C just after reduced pressure concentration and 70 parts by mass of resin n which had been slowly cooled to about 170°C just after reduced pressure concentration, 5 parts by mass of triethylenediamine was added to 100 parts by mass of the mixture and mixed to obtain an organic binder for a casting mold (Example 23).

[0078] -Example 24-

[0079] To a mixture of 50 parts by mass of resin g (a linear phenolic resin modified with a modification rate of 30%) which has just been concentrated under reduced pressure and then slowly cooled to about 170°C and 50 parts by mass of resin h (a linear phenolic resin modified with a modification rate of 30%) which has just been concentrated under reduced pressure and then slowly cooled to about 170°C, 5 parts by mass of triethylenediamine is added to 100 parts by mass of the above mixture and mixed to obtain an organic binder for casting (Example 24).

[0080] -Comparative Example 1-

[0081] Only resin n (novolak resin) was used to form a mold binder (Comparative Example 1).

[0082] -Comparative Example 2-

[0083] Only resin a (o-cresol-modified novolac resin having a modification rate of 30%) was used to form a mold binder (Comparative Example 2).

[0084] -Comparative Example 3-

[0085] To resin n (novolak resin) having been slowly cooled to about 170° C. immediately after reduced pressure concentration, 5 parts by mass of triethylenediamine was added and mixed with respect to 100 parts by mass of resin n to obtain an organic binder for a casting mold (Comparative Example 3).

[0086] -Manufacturing of RCS using organic binder for mold-

[0087] 7000 parts of Flattery silica sand heated to 145°C were added to a pulsating sand mixer, and 105 parts by mass of the organic binder for casting obtained above were further added. The mixture was mixed until the sand particles disintegrated, and then cooled by air supply. Then, 7 parts of calcium stearate were further added to obtain RCS for shell molds using each organic binder for casting.

[0088] - Determination of flexural strength -

[0089] Using each RCS obtained as described above, JIS test pieces (10 mm × 10 mm × 60 mm, sintering conditions: 250°C × 60 seconds) were prepared according to JIS-K-6910. The flexural strength (kgf / cm 2 ). The larger the numerical value shown in the following Tables 1 to 3, the higher the strength of the mold.

[0090] -Measurement of bending (300gf) amount-

[0091] According to the JACT test method: SM-3 bending test method, for each test piece (180mm×40mm×5mm, firing conditions: 250℃×40 seconds) obtained using each RCS, a load of 300gf is applied to the center of the test piece, and the strain (mm) in the center of the test piece after 3 minutes of placement is read with a micrometer, and this value is taken as the bending (300gf) amount. This bending amount (bending amount) is a target index indicating the operability of the mold just after molding and the mold hardening speed. The smaller the value shown in Tables 1 to 3 below, the faster the hardening speed of the mold and the better the operability.

[0092] -Determination of RCS welding point-

[0093] The fusion temperature of each RCS was measured according to the JACT test method: C-1 (fusion point test method). The larger the numerical value shown in the following Tables 1 to 3, the better the anti-blocking property of the RCS.

[0094] [Table 1]

[0095]

[0096] [Table 2]

[0097]

[0098] [Table 3]

[0099]

[0100] Before confirming the effect of the present invention, when comparing Comparative Example 1, which is an organic binder for a mold composed of only a novolac resin (resin n), and Comparative Example 2, which is an organic binder for a mold composed of only an ortho-cresol-modified novolac resin (resin a) with a modification rate of 30%, it was confirmed that in Comparative Example 2, the strength of the mold finally obtained was improved, but the value of the bending amount was large and the curing speed of the mold was slow. Under this understanding, the results of Examples 1 to 24 were studied, and it was confirmed that, for the RCS obtained using the organic binder for a mold according to the present invention, i) the mold obtained therefrom exhibited superior strength compared to the mold formed by the RCS using the organic binder for a mold containing only the novolac resin (resin n) (Comparative Example 1), and ii) the curing speed during mold molding was faster than the RCS using the organic binder for a mold containing only the ortho-cresol-modified novolac resin (resin a) (Comparative Example 2).

Claims

1. An organic binder for a casting mold, characterized in that: The resin binder contains one or more resins selected from the group consisting of cresol-modified novolac resins, novolac-type cresol resins, xylenol-modified novolac resins and novolac-type xylenol resins, and contains triethylenediamine. 2 . The organic binder for a casting mold according to claim 1 , further comprising an aromatic carboxylic acid.

3. The organic binder for casting mold according to claim 1 or claim 2, wherein The triethylenediamine is contained in a ratio of 0.5 to 20 parts by mass based on 100 parts by mass of the resin binder component.

4. The organic binder for a casting mold according to claim 2, wherein The aromatic carboxylic acid is contained in a ratio of 0.5 to 5 parts by mass based on 100 parts by mass of the resin binder component.

5. The organic binder for casting mold according to claim 2, 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.

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

7. A casting mold, which is formed by molding and hardening the molding sand composition according to claim 6.

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