Mold-forming binding agent composition and method for manufacturing mold using same

Abstract

Provided is a mold-forming binding agent composition that can suppress cracking of a mold and can increase the final mold strength by increasing the initial strength of the mold through an increase in the curing rate of the mold and by increasing the flexibility of the mold during mold removal without depending on the nitrogen content. This mold-forming binding agent composition comprises: a furan resin containing a furfuryl alcohol-urea-aldehyde condensate and a furfuryl alcohol-aldehyde condensate; a furfuryl alcohol; and a methyl methacrylate-based resin.

Description

Binder composition for mold molding and method for manufacturing a mold using the same

[0001] The present invention relates to a binder composition for mold molding and a method for manufacturing a mold using the same.

[0002] Acid-curable self-hardening molds are produced by kneading a mixture obtained by kneading refractory particles such as silica sand, a binder for mold molding containing an acid-curable resin such as a furan resin, and a curing catalyst containing sulfuric acid, phosphoric acid, organic sulfonic acid, etc. into a prototype such as a wooden mold or a resin mold, and curing the acid-curable resin. One of the important factors in manufacturing self-hardening molds is the productivity of the molds.

[0003] In order to improve the productivity of the mold, it is necessary to increase the curing rate of the mixture after filling the prototype with the mixture and shorten the time required to remove the mold from the prototype (demolding time). When the curing rate of the mixture is slow, the strength of the mold (so-called initial strength) at the time when the ideal demolding time (for example, 30 minutes) has elapsed since filling becomes low. Since it is necessary to demold after the strength of the mold reaches the level required for demolding, the decrease in the initial strength naturally leads to an increase in the demolding time.

[0004] Patent Document 1 describes "a composition for self-hardening mold consisting of casting sand, a thermoplastic polymer, furfuryl alcohol and an acid curing agent". In Patent Document 1, by using a binder composition composed of a thermoplastic polymer and furfuryl alcohol, the curing rate of the mixture is increased, thereby improving the initial strength of the mold and aiming to shorten the demolding time.

[0005] In addition, in order to improve the productivity of the mold, it is also effective to improve the flexibility of the mold at the time of demolding. If the flexibility of the mold is high, it is possible to prevent mold cracking due to stress concentration in the thin part of the mold when removing the mold from the prototype. If the mold crack cannot be repaired by correction, it is necessary to manufacture the mold again, which deteriorates the productivity.

[0006] Patent Document 2 describes a mold binder composition comprising an acid-curable resin (furan-based resin) blended with a ketone resin, which is a condensate of a specific ketone and an aldehyde. Patent Document 2 does not address the flexibility of the mold during removal, but aims to reduce the likelihood of hot cracking in the casting during pouring by increasing the flexibility of the mold during pouring.

[0007] Furthermore, Patent Document 3 describes a mold-forming binder composition containing a furan resin and a phenol resin having a specific weight-average molecular weight. According to the composition described in Patent Document 3, it is possible to increase the curing speed of the mold, increase the flexibility of the mold during removal, and increase the final strength of the mold. In particular, Patent Document 3 states that the amino groups of urea derived from the furan resin contribute to the flexibility of the mold, and focuses on the nitrogen content in the composition as an indicator of the amino group content, ensuring the flexibility of the mold by increasing the nitrogen content in the composition to 2.2 to 3.5% by mass.

[0008] Japanese Patent Publication No. 53-30421, Japanese Patent Publication No. 62-179847, Japanese Patent Publication No. 2011-131236

[0009] However, the binder composition described in Patent Document 1 consists of a thermoplastic polymer and furfuryl alcohol, and although it contributes to improving the initial strength of the mold, it cannot increase the final strength of the mold, which presents a problem in that it is difficult to apply to molds that require high strength.

[0010] Furthermore, while the binder composition described in Patent Document 2 can increase the flexibility of the mold during pouring, it is insufficient to increase the flexibility of the mold during removal, and under certain conditions, there is a problem that the mold may crack.

[0011] While the binder composition described in Patent Document 3 is excellent in that it enhances the flexibility of the mold during mold removal, this is achieved by increasing the nitrogen content in the composition to 2.2 to 3.5% by mass. However, a high nitrogen content in the composition raises concerns about inducing gas defects when manufacturing certain castings such as cast steel. Therefore, there was a problem in that it was not possible to enhance the flexibility of the mold without relying on the nitrogen content in the composition.

[0012] In view of the above problems, the present invention aims to provide a mold-forming binder composition that can increase the initial strength of a mold by increasing the hardening speed of the mold, suppress mold cracking by increasing the flexibility of the mold during removal regardless of the nitrogen content, and increase the final strength of the mold, and a method for manufacturing a mold using the same.

[0013] In order to solve the above problems, the inventors conducted diligent research and found that the above problems can be solved by a mold-forming binder composition mainly containing a specific furan resin, furfuryl alcohol, and a methyl methacrylate resin.

[0014] Based on the above findings, the gist of the present invention is as follows: [1] A mold-forming binder composition containing a furan resin containing a furfuryl alcohol / urea / aldehyde condensate and a furfuryl alcohol / aldehyde condensate, furfuryl alcohol, and a methyl methacrylate resin.

[0015] [2] The mold-forming binder composition according to [1], wherein the content of the methyl methacrylate resin is 1.0% by mass or more and 10.0% by mass or less.

[0016] [3] A mold-forming binder composition according to [1] or [2] above, wherein the nitrogen content is 1.0% by mass or more and 4.0% by mass or less.

[0017] [4] The mold-forming binder composition according to any one of the above [1] to [3], wherein the weight-average molecular weight of the methyl methacrylate resin is 220,000 or more and 310,000 or less.

[0018] [5] A method for producing a mold, comprising the steps of: mixing a mold-forming binder composition described in any one of the above items [1] to [4] with refractory particles and a curing catalyst to obtain a mixture; and curing the mixture to obtain a mold.

[0019] The present invention provides a binder composition for mold making and a method for manufacturing a mold using the same, which increases the initial strength of the mold by increasing the hardening speed of the mold, suppresses cracking of the mold by increasing the flexibility of the mold during removal regardless of the nitrogen content, and increases the final strength of the mold.

[0020] [Mold-forming binder composition] A mold-forming binder composition according to one embodiment of the present invention (hereinafter also simply referred to as "the composition") contains a furan resin containing a furfuryl alcohol-urea-aldehyde condensate and a furfuryl alcohol-aldehyde condensate, furfuryl alcohol, and a methyl methacrylate resin.

[0021] (Furan Resin) The composition of this embodiment contains a furan resin as an acid-curable resin from the viewpoint of increasing the strength of the final mold. In this embodiment, the furan resin includes a furfuryl alcohol-urea-aldehyde condensate and a furfuryl alcohol-aldehyde condensate as essential components. The composition ratio of the furfuryl alcohol-urea-aldehyde condensate and the furfuryl alcohol-aldehyde condensate in the furan resin is not particularly limited and may be determined as appropriate, for example, from the viewpoint of making the nitrogen content in the composition described later a desired value.

[0022] Examples of the aldehydes mentioned above include formaldehyde, acetaldehyde, glyoxal, furfural, and terephthalaldehyde, and one or more selected from this group can be used. From the viewpoint of mold strength, formaldehyde is preferred.

[0023] When producing a furfuryl alcohol-aldehyde condensate, it is preferable to use 0.01 to 1.0 moles of aldehydes per mole of furfuryl alcohol. When producing a furfuryl alcohol-urea-aldehyde condensate, it is preferable to use 0.01 to 1.0 moles of urea and 0.01 to 1.0 moles of aldehydes per mole of furfuryl alcohol.

[0024] In this embodiment, furan resin is an essential component for increasing the final strength of the mold. From the viewpoint of fully obtaining this effect, the content of furan resin in the composition is preferably 5.0% by mass or more, more preferably 7.0% by mass or more, and even more preferably 10.0% by mass or more. On the other hand, if the content of furan resin is excessive, the content of other components cannot be sufficiently secured, which is undesirable from the viewpoint of the initial strength of the mold and the flexibility of the mold during demolding. Therefore, the content of furan resin in the composition is preferably 27.0% by mass or less, more preferably 25.0% by mass or less, and even more preferably 23.0% by mass or less.

[0025] (Furfuryl alcohol) The composition of this embodiment contains furfuryl alcohol (2-furylmethanol) from the viewpoint of increasing the initial strength of the mold by increasing the hardening speed of the mold. From the viewpoint of fully obtaining this effect, the content of furfuryl alcohol in the composition is preferably 45.0% by mass or more, more preferably 50.0% by mass or more, and even more preferably 55.0% by mass or more. On the other hand, if the content of furfuryl alcohol is excessive, the content of other components cannot be sufficiently secured, which is undesirable from the viewpoint of the flexibility of the mold during demolding and the final strength of the mold. Therefore, the content of furfuryl alcohol in the composition is preferably 90.0% by mass or less, more preferably 85.0% by mass or less, and even more preferably 85.0% by mass or less.

[0026] (Methyl methacrylate resin) The composition of this embodiment contains a methyl methacrylate resin in order to increase the initial strength of the mold by increasing the curing speed of the mold, and to suppress cracking of the mold by increasing the flexibility of the mold during demolding, regardless of the nitrogen content. In this embodiment, the methyl methacrylate resin is dissolved in furfuryl alcohol, and it is presumed that the highly flexible nature of the methyl methacrylate resin has a favorable effect on improving the flexibility of the mold during demolding.

[0027] The weight-average molecular weight of the methyl methacrylate resin is preferably 220,000 or more, more preferably 230,000 or more, even more preferably 240,000 or more, and most preferably 250,000 or more, from the viewpoint of mold flexibility and mold strength. The weight-average molecular weight of the methyl methacrylate resin is preferably 310,000 or less, more preferably 300,000 or less, even more preferably 290,000 or less, and most preferably 280,000 or less, from the viewpoint of solubility in furfuryl alcohol. The weight-average molecular weight (Mw) of the methyl methacrylate resin is obtained in polystyrene equivalent by gel permeation chromatography (GPC). The specific method for measuring the weight-average molecular weight will be explained in the examples described later.

[0028] Methyl methacrylate resins contain methyl methacrylate units and acrylic acid ester units as constituent units. In this specification, "methyl methacrylate unit" refers to a constituent unit derived from methyl methacrylate monomer, and "acrylic acid ester unit" refers to a constituent unit derived from acrylic acid ester monomer.

[0029] Examples of acrylic acid ester units include methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate, among which butyl acrylate is particularly preferred. Butyl acrylate has a significant effect in lowering the glass transition temperature of methyl methacrylate resins and is highly effective in improving the flexibility of molds.

[0030] In methyl methacrylate resins, it is preferable that, per 100.0 parts by mass of the total amount of methyl methacrylate units and acrylic acid ester units, (a) the content of methyl methacrylate units is more than 97.0 parts by mass and 99.0 parts by mass or less, and the content of acrylic acid ester units is 1.0 part by mass or more and less than 3.0 parts by mass; (b) the content of methyl methacrylate units is more than 97.0 parts by mass and 98.5 parts by mass or less, and the content of acrylic acid ester units is 1.5 parts by mass or more and less than 3.0 parts by mass; (c) the content of methyl methacrylate units is more than 97.0 parts by mass and 98.0 parts by mass or less, and the content of acrylic acid ester units is 2.0 parts by mass or more and less than 3.0 parts by mass; and (d) the content of methyl methacrylate units is 97.5 parts by mass and the content of acrylic acid ester units is 2.5 parts by mass. When the content of methyl methacrylate units and acrylic acid ester units in a methyl methacrylate resin is within the ranges described above, it has the advantage of good solubility in furfuryl alcohol and high strength in the final mold.

[0031] In this embodiment, the methyl methacrylate resin is an essential component for obtaining the effect of increasing the initial strength of the mold by increasing the curing speed of the mold, and the effect of suppressing mold cracking by increasing the flexibility of the mold during demolding, regardless of the nitrogen content. From the viewpoint of obtaining these effects sufficiently, the content of the methyl methacrylate resin in the composition is preferably 1.0% by mass or more, more preferably 2.5% by mass or more, and even more preferably 4.5% by mass or more. On the other hand, if the content of the methyl methacrylate resin is excessive, the content of other components cannot be sufficiently secured, which is undesirable from the viewpoint of the initial strength of the mold and the final strength of the mold. Therefore, the content of the methyl methacrylate resin in the composition is preferably 10.0% by mass or less, more preferably 7.5% by mass or less, and even more preferably 5.5% by mass or less.

[0032] (Nitrogen content in the composition) As described above, the composition of this embodiment mainly contains furan resin, furfuryl alcohol, and methyl methacrylate resin, so the flexibility of the mold during mold making can be increased regardless of the nitrogen content in the composition. For this reason, the nitrogen content in the composition is not particularly limited. However, from the viewpoint of increasing the initial strength of the mold, the nitrogen content of the composition is preferably 1.0% by mass or more, more preferably 1.2% by mass or more, and even more preferably 1.4% by mass or more. Furthermore, from the viewpoint of increasing the final strength of the mold, the nitrogen content of the composition is preferably 4.0% by mass or less, more preferably 3.6% by mass or less, even more preferably 2.6% by mass or less, even more preferably 2.1% by mass or less, and most preferably 2.0% by mass or less.

[0033] The nitrogen content in the composition can be adjusted by controlling the amount of nitrogen-containing compounds in the composition. Examples of nitrogen-containing compounds in the composition include furfuryl alcohol, urea, and aldehyde condensates contained in furan resin. The nitrogen content in the composition can be measured by titration according to the factory wastewater testing method in accordance with JIS K 0102-2:2022 (Test method for organic nitrogen).

[0034] (Moisture) The composition of this embodiment may contain moisture. For example, when synthesizing various condensates such as furfuryl alcohol aldehyde condensates, aqueous raw materials are used, and condensation water is generated. For this reason, condensates are usually obtained in the form of a mixture with moisture, but when using such condensates in a composition, it is not necessary to remove this moisture derived from the synthesis process. Furthermore, moisture may be added to adjust the viscosity of the composition to a level that is easy to handle. From the viewpoint of ease of handling and curing speed, the moisture content in the composition is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 3.0% by mass or more. However, if the moisture content is excessive, it will inhibit the curing reaction of the furan resin. For this reason, the moisture content in the composition is preferably 20.0% by mass or less, more preferably 16.0% by mass or less, even more preferably 10.0% by mass or less, and most preferably 7.0% by mass or less.

[0035] (Other components) The composition of this embodiment may contain components other than those listed above. Other components may include silane coupling agents and curing accelerators, and may contain one or both of these.

[0036] The inclusion of a silane coupling agent in the composition is preferable because it can improve the strength of the mold. Examples of silane coupling agents include aminosilanes such as N-β(aminoethyl)γ-aminopropyldimethoxysilane, N-β(aminoethyl)γ-aminopropyltrimethoxysilane, and N-β(aminoethyl)γ-aminopropyltriethoxysilane, and epoxysilanes such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane. One or more selected from this group can be used. From the viewpoint of the final strength of the mold, the content of the silane coupling agent in the composition is preferably 0.01% by mass or more, and more preferably 0.05% by mass or more. Furthermore, from the viewpoint of cost, the content of the silane coupling agent in the composition is preferably 1.2% by mass or less, and more preferably 0.9% by mass or less.

[0037] As a curing accelerator, phenol derivatives are preferred, such as resorcinol, cresol, hydroquinone, bisphenol A, bisphenol F, etc., and one or more selected from the group consisting of these can be used. Among these, resorcinol is preferred from the viewpoint of improving the strength of the final mold. The content of the phenol derivative in the composition is preferably 1.0% by mass or more, more preferably 2.0% by mass or more, and even more preferably 3.0% by mass or more, from the viewpoint of the solubility of the phenol derivative in furfuryl alcohol and improving the strength of the final mold. From a cost viewpoint, the content of the phenol derivative in the composition is preferably 10.0% by mass or less, more preferably 8.0% by mass or less, and even more preferably 6.0% by mass or less.

[0038] The composition of this embodiment preferably consists of the above-mentioned essential component, a furan resin, furfuryl alcohol, and a methyl methacrylate resin, and more preferably consists of the above-mentioned essential component and one or more of the above-mentioned optional components selected from the group consisting of water, a silane coupling agent, and a curing accelerator.

[0039] [Method for manufacturing a mold] A method for manufacturing a mold according to one embodiment of the present invention comprises the steps of: mixing the mold-forming binder composition according to the above embodiment of the present invention with refractory particles and a curing catalyst to obtain a mixture; and curing the mixture to obtain a mold.

[0040] In the mold manufacturing method of this embodiment, the mold can be manufactured by using the same process as conventional mold manufacturing methods. For example, the above mixture (mixed sand) can be obtained by adding the composition of this embodiment and a curing catalyst for hardening the composition to refractory particles and kneading them in a batch mixer or continuous mixer. In this embodiment, from the viewpoint of ensuring a pot life, it is preferable to add the composition after adding the curing catalyst to the refractory particles.

[0041] Examples of refractory particles include silica sand, chromite sand, zircon sand, olivine sand, alumina sand, mullite sand, and synthetic mullite sand. One or more of these can be selected from the group. In addition, used refractory granular particles that have been recovered or recycled can also be used.

[0042] As the curing catalyst, one or more conventionally known ones can be used, such as organic sulfonic acids including xylene sulfonic acid and toluene sulfonic acid, or acidic aqueous solutions containing phosphoric acid, sulfuric acid, etc. Furthermore, the curing catalyst may contain one or more solvents selected from the group consisting of alcohols and esters, or carboxylic acids. Among these, alcohols are more preferred from the viewpoint of improving the strength of the final mold. In addition, the inclusion of the above solvents and carboxylic acids reduces the water content in the curing catalyst, further improving the strength of the final mold. From the viewpoint of improving the strength of the final mold, the content of the solvents and carboxylic acids in the curing catalyst is preferably 5 to 50% by mass, and more preferably 10 to 40% by mass.

[0043] From the perspective of ultimately improving the mold strength, as the alcohols, one or more selected from propanol, butanol, pentanol, hexanol, heptanol, octanol, and benzyl alcohol are preferable. From the perspective of reducing the viscosity of the curing catalyst, it is preferable to contain methanol or ethanol. As the esters, it is preferable to use one or both of butyl acetate and butyl benzoate. As the carboxylic acids, from the perspectives of improving the strength of the final mold and reducing the odor, carboxylic acids having a hydroxyl group are preferable, and it is more preferable to use one or more selected from lactic acid, citric acid, and malic acid.

[0044] The content ratios of the refractory particles, the composition, and the curing catalyst in the mixture can be set as appropriate. However, with respect to 100 parts by mass of the refractory particles, the content of the composition is preferably in the range of 0.5 to 1.5 parts by mass, and the content of the curing catalyst is preferably in the range of 0.07 to 1.0 parts by mass. With such ratios, sufficient mold strength can be obtained.

[0045] From the perspective of minimizing the amount of moisture contained in the mold as much as possible and from the perspective of the mixing ratio in the mixer, the content of the curing catalyst is preferably 10 to 50 parts by mass, more preferably 15 to 45 parts by mass, and even more preferably 20 to 40 parts by mass with respect to 100 parts by mass of the composition.

[0046] [Raw materials of the composition] <Furan resin> As furan resin 1, GFA-500 (nitrogen content 3.1% by mass, moisture 18.0% by mass) manufactured by Gun Ei Chemical Industry Co., Ltd. was prepared. As furan resin 2, FDF-280 (nitrogen 4.1% by mass, moisture 18.0% by mass) manufactured by Jinan Shengquan Group Share Holding Co., Ltd. was prepared.

[0047] <Furfuryl alcohol> 2-Furylmethanol (pure grade) manufactured by Junsei Chemical Co., Ltd. was prepared.

[0048] <Methyl methacrylate resin> Methyl methacrylate resins at three levels with weight average molecular weights of 220,000, 265,000, and 310,000 (product name: Kaneparl (registered trademark) AX manufactured by Kaneka Corporation) were prepared.

[0049] The weight-average molecular weight obtained by the following method was used as the weight-average molecular weight of the methyl methacrylate resin. (1) 0.02 g of resin was dissolved in 20 mL of tetrahydrofuran (THF). (2) The gel component in the resulting solution was then filtered. (3) Next, only the THF-soluble component (filtrate) was used as the sample, and GPC measurements were performed using a gel permutation chromatograph (GPC) under the following conditions. (4) The weight-average molecular weight (Mw) and number-average molecular weight (Mn) were calculated from the measurement chart obtained from the GPC measurement. Note that the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are relative values ​​in terms of polystyrene. <GPC Measurement Conditions> Measurement device: Tosoh Corporation, high-speed GPC instrument HLC-8220 Columns used: Tosoh Corporation, Super HZM-H x 2, Super H-RC x 2 Column temperature: 40°C, Mobile phase: THF (tetrahydrofuran) Flow rate: 0.35 mL / min Injection volume: 10 μL Detector: RI

[0050] <Silane coupling agent> N-β(aminoethyl)γ-aminopropyldimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.) was prepared.

[0051] [Preparation of Composition] (Examples No. 1-9, 14-15 using furan resin 1) Furfuryl alcohol in the quantities (parts by mass) listed in Table 1 and methyl methacrylate resin in the weight-average molecular weight and quantity (parts by mass) listed in Table 1 were added to a flask equipped with a thermometer, condenser, and stirrer, and the mixture was stirred at 25°C for 20 minutes to dissolve. Then, silane coupling agent in the quantities (parts by mass) listed in Table 1 was added to obtain an intermediate composition. Furan resin 1 in the quantities (parts by mass) shown in Table 1 was added to the obtained intermediate composition and mixed to obtain the composition.

[0052] (Examples No. 10-13 using furan resin 2) In a flask equipped with a thermometer, condenser, and stirrer, the following were added: furan resin 2 in the quantities (parts by mass) shown in Table 1, furfuryl alcohol in the quantities (parts by mass) shown in Table 1, and methyl methacrylate resin in the weight-average molecular weight and quantities (parts by mass) shown in Table 1. The mixture was stirred at 35°C for 20 minutes to dissolve. Then, the following were added and mixed: silane coupling agent in the quantities (parts by mass) shown in Table 1 and water (water only in No. 10) to obtain the composition.

[0053] (Comparative Example No. 16) In a flask equipped with a thermometer, a condenser, and a stirrer, furfuryl alcohol in the amount (parts by mass) shown in Table 1 and silane coupling agent in the amount (parts by mass) shown in Table 1 were mixed to obtain an intermediate composition. Furan resin 1 in the amount (parts by mass) shown in Table 1 was added to the obtained intermediate composition and mixed to obtain a composition.

[0054] (Comparative Example No. 17) In a flask equipped with a thermometer, condenser, and stirrer, the amount (parts by mass) of furfuryl alcohol and the weight-average molecular weight and amount (parts by mass) of methyl methacrylate resin listed in Table 1 were added and stirred at 25°C for 20 minutes to dissolve. Then, the amount (parts by mass) of silane coupling agent listed in Table 1 was added and mixed to obtain the composition.

[0055] [Content of each component in the composition] Table 2 shows the content (mass%) of furan resin, furfuryl alcohol, methyl methacrylate resin, water, and silane coupling agent in the composition. The water content in the composition was measured using the method for measuring the water content of chemical products in accordance with JIS K 0068:2001 (Karl Fischer moisture method). In addition, the nitrogen content in the composition was measured using the titration method of the factory wastewater test method in accordance with JIS K 0102-2:2022 (Test method for organic nitrogen) and is shown in Table 2.

[0056] [Preparation of the mixture] To 100 parts by mass of recycled furan sand (a mixture of 85 parts by mass of No. 5 silica sand manufactured by Tohoku Silica Sand Co., Ltd. and 15 parts by mass of Espal #35L manufactured by Yamakawa Sangyo Co., Ltd.), 0.7 parts by mass of the previously obtained composition and 0.28 parts by mass of a hardening catalyst (70% by mass of p-toluenesulfonic acid) were added and kneaded to obtain the mixture. As the recycled furan sand used, the weight loss rate (L.O.I) when heated at 1000°C for 1 hour in the open atmosphere was 2.8% by mass.

[0057] [Evaluation of initial mold strength (compressive strength after 30 minutes)] The mixture immediately after kneading was filled into a cylindrical test piece frame with a diameter of 50 mm and a height of 50 mm, and allowed to harden under conditions of 25°C and 60% relative humidity. After 30 minutes from filling, the mold was removed and the test piece was taken out (removal time 30 minutes). The compressive strength of the test piece immediately after removal was measured using a benchtop pressure resistance tester (manufactured by Gun-ei Chemical Industry Co., Ltd.) in accordance with JIS Z 2601:1993 (Compressive strength test method). The results are shown in Table 2.

[0058] [Evaluation of final mold strength (compressive strength after 24 hours)] The mixture immediately after mixing was filled into a cylindrical test piece frame with a diameter of 50 mm and a height of 50 mm, and cured under conditions of a temperature of 25°C and a relative humidity of 60%. After 30 minutes from filling, the mold was removed and the test piece was taken out (removal time 30 minutes). After 24 hours from removal, the compressive strength of the test piece was measured using a benchtop pressure resistance tester (manufactured by Gun-ei Chemical Industry Co., Ltd.) in accordance with JIS Z 2601:1993 (Compressive strength test method). The results are shown in Table 2.

[0059] [Evaluation of mold flexibility during demolding (maximum point displacement during demolding)] The mixture immediately after mixing was filled into a rectangular test piece frame measuring 80 mm in length, 30 mm in width, and 10 mm in height. The mixture was allowed to harden under conditions of 25°C and 60% relative humidity. After 30 minutes from filling, the mold was demolded and the test piece was removed (demolition time: 30 minutes). The three-point bending strength of the test piece immediately after demolding (head speed: 5 mm / min, distance between supports: 60 mm) was measured, and the maximum point displacement (mm), which represents the deflection of the rectangular test piece until it reached that maximum point strength, was measured. A larger maximum point displacement indicates higher mold flexibility during demolding. The results are shown in Table 2.

[0060]

[0061]

[0062] As is clear from Table 2, Invention Examples No. 1 to 15 were excellent in terms of initial mold strength, final mold strength, and mold flexibility during demolding. In contrast, Comparative Example No. 16, which did not contain methyl methacrylate resin, was inferior in both initial mold strength and mold flexibility during demolding. Furthermore, Comparative Example No. 17, which did not contain furan resin, was inferior in final mold strength.

[0063] The mold-forming binder composition according to the present invention can be used as a raw material for self-hardening molds used in wooden pattern casting and full-mold casting.

Claims

1. A mold-forming binder composition containing a furfuryl alcohol / urea / aldehyde condensate and a furan resin containing a furfuryl alcohol / aldehyde condensate, furfuryl alcohol, and a methyl methacrylate resin.

2. The mold-forming binder composition according to claim 1, wherein the content of the methyl methacrylate resin is 1.0% by mass or more and 10.0% by mass or less.

3. The mold-forming binder composition according to claim 1, wherein the nitrogen content is 1.0% by mass or more and 4.0% by mass or less.

4. The mold-forming binder composition according to claim 1, wherein the weight-average molecular weight of the methyl methacrylate resin is 220,000 or more and 310,000 or less.

5. A method for producing a mold, comprising the steps of: mixing a mold-forming binder composition according to any one of claims 1 to 4, refractory particles, and a curing catalyst to obtain a mixture; and curing the mixture to obtain a mold.

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