Casting sand for three-dimensional laminated molding and method for producing the same

Abstract

Provided is a casting sand for additive manufacturing that can provide a mold that is difficult to deform even when a water-based coating agent is used. 【Solution means】 It is a casting sand used for three-dimensional additive manufacturing, (1) the particles constituting the casting sand include (a) sand grains and (b) an organic layer formed on the surface of the sand grains, and (2) the organic layer contains a furan resin precursor or a fatty acid having a melting point of 40 to 75 °C and a heteropolyacid. It relates to a casting sand for three-dimensional additive manufacturing characterized by this.

Description

Technical Field

[0001] The present invention relates to a novel casting sand for three-dimensional laminated molding and a method for manufacturing the same. In particular, it relates to casting sand supplied to a three-dimensional laminated molding machine, which is a sand mold machine for casting, and a method for manufacturing the same.

Background Art

[0002] The laminated molding method is a technique for producing a molded body by stacking sliced two-dimensional layers based on three-dimensional data such as 3D-CAD. In practice, an object having a desired shape can be created by laminating a three-dimensional laminated molding material with a 3D printer. As the three-dimensional laminated molding material, various materials such as metals, resins, sands, gypsums, and ceramics are used.

[0003] Among these, since sand can be suitably used as a sand mold as a mold, the sand mold is also manufactured by the laminated molding method. In particular, in recent years, three-dimensional laminated molding technology that can directly realize a three-dimensional shape created by 3D-CAD or the like as a sand mold has attracted attention. In such a method for manufacturing a sand mold, various manufacturing methods or three-dimensional laminated molding materials have been proposed for the purpose of improving defects in the sand mold, improving laminated fluidity, and the like.

[0004] In Patent Document 1, a casting sand including sand and a solid acid catalyst mixed with the sand is proposed, which can cause the binder to cure early when the binder is added to the casting sand, and can efficiently mold a sand mold.

[0005] However, in the above casting sand, the solid acid catalyst is not uniformly dispersed throughout the sand, and when the binder is added, unevenness (distribution) occurs in the curing of the furan resin precursor, making it difficult to increase the strength of the sand mold. Also, in order to increase the strength, a method of increasing the addition amounts of furan resin, hardener, etc., which is commonly used in self-hardening furan sand molds, is not applicable to this technology.

[0006] In addition, when manufacturing a three-dimensional laminated object using the casting sand produced by the above method, when a binder is applied to the laminated casting sand, the applied binder comes into contact with the solid acid catalyst, which is a curing agent, on the surface of the casting sand, and a curing reaction immediately occurs. For this reason, although the initial strength of the sand mold is developed to a certain extent, when the amount of the binder is small, the binder gradually solidifies before covering the entire casting sand grains, so no further increase in strength can be expected.

[0007] Furthermore, regarding the method for manufacturing the casting sand, two types of solid acid catalysts with different particle size distributions are prepared and mixed with sand to obtain the casting sand. This is to improve the filling property when manufacturing a three-dimensional laminated object, but paying attention to the particle size distribution of the solid acid catalyst complicates the method for manufacturing the casting sand.

[0008] In addition to the above literature, for example, a method for manufacturing a sand mold is known that includes a step of mixing a solid carboxylic acid with refractory particles, a refractory particle layer forming step of forming a refractory particle layer including the refractory particles mixed with the solid carboxylic acid, and a binder composition supply step of providing a binder composition including a resin in which the solid carboxylic acid acts as a curing agent to a desired region of the refractory particle layer, and sequentially repeating the refractory particle layer forming step and the binder composition supply process (Patent Document 2).

[0009] In particular, in the casting sand, a method is described in which the solid carboxylic acid is dissolved in a solvent in the process of adding the solid carboxylic acid to the refractory particles, then the refractory particles are mixed, and the solvent is volatilized and removed to obtain the casting sand.

[0010] However, since the solid carboxylic acid has low affinity with the solvent, it cannot be uniformly present in the solvent. It is impossible to uniformly disperse the solid carboxylic acid on the surface of the refractory particles when a solution in such a state is mixed with the refractory particles.

[0011] Moreover, since the solid carboxylic acid only adheres to the surface of the refractory particles with a weak force, the solid carboxylic acid is peeled off from the refractory particles and falls due to the physical friction between the refractory particles occurring inside the apparatus such as the recoater of the three-dimensional laminating molding machine, and the stability of strength expression cannot be expected.

[0012] After laying a material in which polycarboxylic acids are mixed with a refractory granular material in layers, the step of injecting a sugar binder into a desired region of the material laid in layers is repeated until a three-dimensional laminated molded object is molded. After completion of the molding, a production method is known in which the sugar binder is cured by heating the three-dimensional laminated molded object (Patent Document 3).

[0013] However, in this method, since the substances constituting the three-dimensional laminated molded object are only polycarboxylic acids and a sugar binder, the heat resistance is lower than that of a sand mold using a furan resin precursor. For this reason, it is impossible to use it as a sand mold for casting iron-based materials with a relatively high melting temperature.

[0014] In addition, Patent Document 3 describes a method of promoting the curing reaction of a sugar binder and polycarboxylic acids by heating at 150°C or higher in order to exhibit practical handling strength (that is, for taking out).

[0015] However, in this method, since a curing reaction cannot be expected with the passage of time, it is necessary to apply heat from the outside. Heating for the sand mold removal operation is unnecessary for the process of a self-hardening sand mold, which leads to a decrease in work efficiency.

[0016] On the other hand, in a method for manufacturing a press mold, it is disclosed that a furan resin, which is an acid-curing type organic self-hardening resin, is used as a binder (Patent Document 4).

[0017] However, when applying a furan resin as a binder to sand grains, if an aqueous mold coating agent is used, a problem of sand mold deformation occurs as in the case shown in Patent Document 6 described later.

[0018] In addition, there is also known a technique for improving the strength by exposing a molded body obtained by applying water glass to quartz sand particles as granular materials and curing them by heating to an atmosphere enriched with gaseous water (Patent Document 5).

[0019] However, in the above technique, water glass is used as a binder, and enriched water vapor is required to increase the strength. It is also described that the strength cannot be increased by heating, and the purpose of heating is clearly stated as a means for realizing the enrichment of water vapor. That is, the above technique solely utilizes the principle of water glass solidification. In the present invention, not only is the enrichment of water vapor not required, but there is also no need to consider the firing atmosphere. On the contrary, the enrichment of water vapor and the like have an adverse effect on the curing of the furan resin.

[0020] On the other hand, the applicant of the present application has proposed foundry sand that can provide a sand mold having high strength and high dimensional accuracy, which is used in a method for manufacturing a sand mold by a laminated manufacturing method including a step of forming a layer containing the foundry sand and a step of solidifying a predetermined region of the layer by adding a binder to the predetermined region of the layer in sequence, and has filed a patent application. The foundry sand is characterized in that: (1) a furan resin organic layer containing a furan resin precursor and an acid component is formed on the surface of the sand grains constituting the foundry sand; (2) the solubility of the furan resin organic layer in methanol (25 ° C) is 32% or more.

[0021] Since the furan resin organic film formed on the surface of the foundry sand grains manufactured by such a method is in a semi-cured state, it is possible to cure the furan resin precursor uniformly over the entire foundry sand when adding the binder. In addition, since the foundry sand appears to be in a dry state, even in a lamination method in which the sand cannot be tamped down, insufficient filling of the foundry sand does not occur, so that a sand mold having high strength and high dimensional accuracy can be manufactured.

[0022] However, in Patent Document 6, it may be deformed when applying and drying an aqueous coating agent.

[0023] Generally, when performing iron-based casting, a technique of applying an inorganic material called a coating agent to a sand mold for the purpose of suppressing welding defects and the like is known. In this case, as the coating agent, an aqueous coating agent in the form of a slurry in which powder of an inorganic material is dispersed in an aqueous solvent is generally used. Then, the aqueous coating agent is applied to the sand mold by a method of dipping the sand mold into such an aqueous coating agent (dipping method). Thereafter, it is subjected to a step of dehydration and drying by heating or the like.

[0024] When dipping a sand mold made of conventional casting sand as in Patent Document 6 into a slurry of an aqueous coating agent, since the sand mold absorbs moisture contained in the aqueous coating agent, problems such as deformation or cracking of the sand mold occur during the subsequent drying process. This is presumably because the hardening reaction of the self-hardening furan resin has not sufficiently progressed in the sand mold immediately after laminated molding, and it is presumed that the furan composition during hardening is in a state where it easily absorbs water. That is, when an unhardened part exists in the sand mold and a large amount of water is absorbed by applying the aqueous coating agent, it is considered that the part becomes soft by heat and the sand mold cannot support its own weight and deforms.

[0025] In addition, such problems (phenomena) can occur not only in the technology of Patent Document 6 but also in laminated molding materials laminated by an acid-curing type furan resin.

Prior Art Documents

Patent Documents

[0026]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0027] Therefore, the main object of the present invention is to provide foundry sand for three-dimensional laminated modeling that can provide a sand mold that is difficult to deform even when using an aqueous coating agent. Means for Solving the Problems of the Invention

[0028] As a result of intensive research in view of the problems of the prior art, the present inventor has found that particles (particle groups) having a specific configuration can achieve the above object, and has completed the present invention.

[0029] That is, the present invention relates to the following foundry sand for three-dimensional laminated modeling and a method for manufacturing the same. 1. Foundry sand used for three-dimensional laminated modeling, (1) The particles constituting the foundry sand include (a) sand grains and (b) an organic layer formed on the surface of the sand grains, (2) The organic layer contains a furan resin precursor or a fatty acid having a melting point of 40 to 75°C and a heteropolyacid, Foundry sand for three-dimensional laminated modeling, characterized in that. 2. The foundry sand for three-dimensional laminated modeling according to item 1 above, wherein the heteropolyacid contains at least one of silicotungstic acid and phosphotungstic acid. 3. The foundry sand for three-dimensional laminated modeling according to item 1 above, wherein 0.5 to 2.5 parts by mass of heteropolyacid is contained per 100 parts by mass of sand grains. 4. The foundry sand for three-dimensional laminated modeling according to item 1 above, wherein solid particles of heteropolyacid are supported on a carrier containing a furan resin precursor or a fatty acid having a melting point of 40 to 75°C. 5. The foundry sand for three-dimensional laminated modeling according to item 1, wherein the organic layer has an aqueous wetting layer containing a heteropolyacid formed on the surface of the sand grains and a hydrophobic layer containing a furan resin precursor or a fatty acid having a melting point of 40 to 75°C, and the surface of the aqueous wetting layer is covered by the hydrophobic layer. 6. A kit for three-dimensional laminated modeling, comprising the foundry sand for three-dimensional laminated modeling according to any one of items 1 to 5 and a binder for coating. 7. A method for manufacturing foundry sand for three-dimensional laminated modeling, comprising: (1) A step of obtaining precursor particles coated with a coating layer containing the furan resin precursor or fatty acid on the surface of the sand grains by mixing at least the sand grains and a coating agent containing a furan resin precursor or a fatty acid having a melting point of 40 to 75°C at 100°C or lower, and (2) A step of obtaining composite particles in which the solid particles are supported on the coating layer on the surface of the precursor particles by mixing the precursor particles and solid particles of heteropolyacid at 100°C or lower. A method for manufacturing foundry sand, characterized by including the above steps. 8. A method for manufacturing foundry sand for three-dimensional laminated modeling, comprising: (1) A step of obtaining precursor particles coated with an aqueous wetting layer containing the aqueous solution on the surface of the sand grains by mixing at least the sand grains and an aqueous solution of heteropolyacid at 100°C or lower, (2) A step of obtaining composite particles in which the aqueous wetting layer is covered with a hydrophobic layer containing the fatty acid by mixing the precursor particles and a coating agent containing a furan resin precursor or a fatty acid having a melting point of 40 to 75°C at 100°C or lower. A method for manufacturing foundry sand, characterized by including the above steps. 9. The manufacturing method according to item 7 or 8, further including a step of adding 0.5 part by mass or less of a silane coupling agent to 100 parts by mass of the sand grains. 10. A method for manufacturing a sand mold using the foundry sand for three-dimensional laminated modeling according to any one of items 1 to 5, comprising: (1) A step of obtaining a molded body by repeatedly performing in sequence a step of forming a layer containing the foundry sand and a step of solidifying a predetermined region of the layer by adding a binder for coating to the region, and (2) Obtaining a sand mold by heat-treating the molded body not containing the aqueous coating agent at 40 to 250 °C in the air or an inert gas atmosphere A method for manufacturing a sand mold, characterized by comprising the above. 11. A sand mold for casting iron-based materials, comprising the casting sand for three-dimensional laminated molding according to any one of Items 1 to 5 above. 12. The sand mold for casting iron-based materials according to Item 11 above, further comprising an aqueous coating agent.

Advantages of the Invention

[0030] According to the present invention, it is possible to provide casting sand for three-dimensional laminated molding that can provide a sand mold that is difficult to deform even when using an aqueous coating agent. In particular, it is possible to achieve relatively high sand mold strength and use an aqueous coating agent, and it is also possible to provide casting sand that is good for the working environment. The present invention can be preferably used particularly as casting sand for three-dimensional laminated molding.

[0031] The casting sand in the present invention has an organic layer present on the surface of the sand grains containing a furan resin precursor or a saturated fatty acid and a heteropolyacid as a curing agent. This organic layer is usually in a semi-cured state. By forming such an organic layer on the surface of the sand grains, when a binder for coating is sprayed on the casting sand of the present invention, it can be cured evenly over the entire sand grains, and as a result, a sand mold having high strength can be obtained. In particular, sufficiently high strength can also be obtained even about several minutes (for example, 30 minutes later) after the production of the sand mold.

[0032] In particular, in the present invention, since a heteropolyacid having higher solubility in water than sulfonic acid is used as the curing agent, the heteropolyacid can reach evenly to the central part of the inter-grain bridge forming the cured body of the furan resin precursor, so that higher strength can be obtained and it is possible to contribute to the effect of preventing deformation of the sand mold.

[0033] Thus, even when manufacturing a sand mold by a laminated molding method using the casting sand of the present invention, high strength can be imparted to the sand mold.

[0034] In addition, when the foundry sand of the present invention is in a dry state, even in a stacking method (stack molding method) where it is difficult or impossible to perform the ramming operation of the sand, there is no risk of insufficient filling of the foundry sand, and it is possible to increase the strength of the sand mold.

[0035] Furthermore, since the heteropolyacid used as a hardening agent in the foundry sand of the present invention substantially does not contain a sulfur component, it is possible to avoid the influence of the sulfur component as shown below.

[0036] Generally, a liquid (molten metal) obtained by melting a metal such as iron or aluminum at a high temperature is poured into a sand mold formed of foundry sand to produce a casting. When pouring, sulfur components contained in the foundry sand are thermally decomposed to generate sulfurous acid gas or the like, which has an adverse effect on the environment.

[0037] Moreover, especially when casting iron-based materials, the phenomenon of sulfur penetration into the casting occurs due to the inclusion of sulfur components in the foundry sand (or sand mold). In this case, especially in the case of spheroidal graphite cast iron or the like, poor spheroidization (metallic structure) of graphite is caused, which may lead to a decrease in the strength or toughness of the casting.

[0038] On the other hand, as described above, in the foundry sand of the present invention and the sand mold produced therefrom, the sulfur component content is controlled to be extremely small or 0%, so that the influence of the sulfur component on the working environment, the influence on iron-based materials, etc. can be avoided. Therefore, it can be suitably used for casting iron-based materials with a high melting temperature, which is difficult to handle with conventional sand molds. For example, it can be widely used in the production (casting) of mechanical parts made of cast iron.

[0039] The kit comprising the foundry sand of the present invention having such characteristics and a combination thereof with a coating binder can be suitably used for molding a sand mold by a stacking molding method.

[0040] The foundry sand of the present invention was developed to be particularly suitable for the laminated manufacturing method, but it can also be diverted to so-called self-hardening sand mold materials. In particular, it can also be used as a countermeasure for casting defects such as veining defects in combination with artificial sand and furan resin.

[0041] In addition, according to the method for manufacturing the foundry sand of the present invention, the foundry sand of the present invention can be manufactured more reliably and efficiently. The inventor has obtained the knowledge that in order to obtain high sand mold strength, it is necessary to control the solubility of the organic layer and the reaction water. In particular, as a method for controlling the solubility of the organic layer, it is important to control the water content in the organic layer. Furthermore, by devising a method for dispersing the hardener in the organic layer, a more desirable effect can be obtained. By introducing these into the manufacturing method of the present invention, it is possible to realize stable sand mold strength with a relatively small amount of hardener and resin. On the other hand, compared with dry sand, even for foundry sand with a high humidity in the sand grain gaps but in a state between the dry state and the wet state in terms of appearance (hereinafter, also referred to as the "intermediate state"), since the organic layer is present, the hardener can be uniformly dispersed, so it is possible to exhibit a sufficiently high strength.

Brief Description of the Drawings

[0042]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0043] 1. Foundry Sand for 3D Laminated Manufacturing The casting sand for three-dimensional laminated molding of the present invention (the casting sand of the present invention) is a casting sand used for three-dimensional laminated molding, (1) The particles constituting the casting sand include (a) sand grains and (b) an organic layer formed on the surface of the sand grains, (2) The organic layer contains a furan resin precursor or a fatty acid having a melting point of 40 to 75 °C and a heteropolyacid. It is characterized by this.

[0044] A schematic diagram of the particles of the casting sand of the present invention is shown in FIG. 1. In the casting sand (particles) 10 shown in FIG. 1, an organic layer 12 is formed on the surface of sand grains 11 serving as a core. In particular, it is desirable that substantially the entire surface of the sand grains 11 is covered with the organic layer 12, but as long as the effects of the present invention are not hindered, there may be a portion not covered with the organic layer.

[0045] The organic layer 12 contains a furan resin precursor or a fatty acid having a melting point of 40 to 75 °C and a heteropolyacid. That is, in the present invention, the case of containing a furan resin precursor and a heteropolyacid, the case of containing a fatty acid having a melting point of 40 to 75 °C and a heteropolyacid, etc. are included.

[0046] The structure of the organic layer 12 is not particularly limited, but as a preferred embodiment, (a) a structure in which solid particles of a heteropolyacid are supported on a carrier containing a furan resin precursor or a fatty acid having a melting point of 40 to 75 °C (Embodiment 1), an aqueous wet layer containing a heteropolyacid formed on the surface of the sand grains, and a hydrophobic layer containing a furan resin precursor or a fatty acid having a melting point of 40 to 75 °C, and a structure in which the surface of the aqueous wet layer is covered with the hydrophobic layer (Embodiment 2), etc. can be mentioned.

[0047] Figure 2 shows a schematic diagram of Embodiment 1. The foundry sand 10 shown in Figure 2 has a carrier (carrier layer) 12a containing a furan resin precursor or a fatty acid with a melting point of 40 to 75°C formed around the sand grains 11, and solid particles 12b of heteropolyacid are supported on the carrier. The solid particles 12b of heteropolyacid only need to be fixed to the carrier, may be contained in the carrier, or may be adhered to the surface of the carrier. The properties of the foundry sand according to Embodiment 1 are not limited, but usually it is in a dry state (dry powder state) due to the above structure.

[0048] Figure 3 shows a schematic diagram of Embodiment 2. The foundry sand 10 shown in Figure 3 has a water-wet layer 22a containing heteropolyacid formed around the sand grains 11, and a hydrophobic layer 22b containing a furan resin precursor or a fatty acid with a melting point of 40 to 75°C is formed on the water-wet layer 22a. In this case, since the surface of the water-wet layer 22a is substantially covered by the hydrophobic layer 22b, the evaporation of the moisture contained in the water-wet layer 22a is blocked, so the wet state is maintained. The properties of the foundry sand according to Embodiment 2 are not limited, but usually it is in a wet state (wet kneaded material state) due to the above structure. In this case, the heteropolyacid is contained in the state of a solution (especially an aqueous solution) in the water-wet layer.

[0049] (A) Substances constituting the foundry sand of the present invention (A-1) Sand grains Sand grains (that is, sand grains before being coated with the organic layer) are used as the core of the particles constituting the foundry sand of the present invention. As the sand which is an aggregate of sand grains, either natural silica sand or artificial sand can be used. Examples of artificial sand include mullite, spinel, alumina, etc. In addition, a mixed sand of new sand and calcined recycled sand of natural silica sand may also be used. In the present invention, it is preferable to use new artificial sand from the viewpoint of further suppressing the igloss. In the artificial sand, neither the melting method nor the sintering method is limited.

[0050] The particle size of the sand grains as bone sand is not particularly limited, but generally, an AFS of 35 to 120 is preferred in terms of particle size index, and particularly an AFS of 60 to 100 is more preferred. The particle size can be appropriately adjusted by known classification methods as needed.

[0051] (A-2) Organic layer The organic layer is a film that covers part or all of the surface of the sand grains, and preferably covers the entire sand grains.

[0052] In the casting sand of the present invention, the organic layer is not directly involved in the bonding between the sand grains constituting the casting sand at the stage before laminating the casting sand of the present invention. When the humidity in the sand grain gaps is low, the appearance of the casting sand product of the present invention is in a dry state and has excellent fluidity. On the other hand, even in an intermediate state where the humidity in the sand grain gaps is high, due to the presence of the organic layer, the hardening agent is uniformly dispersed, and since it is in an intermediate state, the filling property is sufficiently high and a practical laminating property can be obtained, so a relatively high strength can be exhibited.

[0053] The organic layer contains (a1) a furan resin precursor or (a2) a fatty acid having a melting point of 40 to 75°C, and (b) a heteropolyacid.

[0054] (a1) Furan resin precursor The furan resin precursor is not limited as long as it can form a furan resin by condensation polymerization or the like. For example, furfuryl alcohol, a furan resin prepolymer, etc. can be mentioned. In particular, for reasons of suppressing the heat of reaction and reducing the viscosity of the resin, it is desirable to use furfuryl alcohol and a furan resin prepolymer in combination.

[0055] Examples of the furan resin prepolymer include a polymer of furfuryl alcohol alone, a copolymer of furfuryl alcohol and an aldehyde compound, a copolymer of furfuryl alcohol, urea, and an aldehyde compound (urea-modified furan resin prepolymer), a copolymer of furfuryl alcohol and furfural, etc. These can be used alone or in combination of two or more.

[0056] In the present invention, a copolymer of furfuryl alcohol, urea, and an aldehyde compound (urea-modified furan resin prepolymer) is particularly preferred because it is easy to increase the strength. Examples of the aldehyde polymer compound include formaldehyde, acetaldehyde, glyoxal, furfural, and the like. In the present invention, formaldehyde is particularly preferred.

[0057] When using furfuryl alcohol and a furan resin prepolymer in combination as the furan resin precursor, with the total of both being 100 parts by mass, the content of furfuryl alcohol is desirably in the range of 35 to 60 parts by mass from the viewpoint of viscosity.

[0058] Also, the content of the furan resin precursor is usually 0.025 to less than 2.2 parts by mass, particularly preferably 0.03 to 2.1 parts by mass, and most preferably 0.1 to 0.3 parts by mass with respect to 100 parts by mass of sand. By setting within such a range, the strength of the obtained sand mold can be more reliably increased.

[0059] The content ratio (solid content) of the furan resin precursor in the organic layer is not particularly limited as long as it is formulated to have the content shown above, but is usually about 1 to 90% by mass, and can further be in the range of about 20 to 90% by mass. Therefore, for example, it can be set to 30 to 60% by mass. Also, for example, it can be 1 to 80% by mass, can be 1.5 to 60% by mass, and can further be set to 5 to 25% by mass.

[0060] (a2) Fatty acid with a melting point of 40 to 75 °C In the cast sand of the present invention, the fatty acid with a melting point of 40 to 75 °C (hereinafter, also simply referred to as "fatty acid") is mainly for coating the surface of sand grains for homogeneous dispersion of the acid component.

[0061] In the present invention, saturated fatty acids having 12 or more carbon atoms (C12) are preferred, and particularly preferred are saturated fatty acids that are solid at normal temperature (40°C or lower) and have a melting point of 40 to 75°C. Among these, it is desirable to use at least one of lauric acid, palmitic acid, and stearic acid.

[0062] The content of the fatty acid is usually 0.015 to less than 1.2 parts by mass, particularly preferably 0.02 to 1.1 parts by mass, and most preferably 0.1 to 0.2 parts by mass with respect to 100 parts by mass of sand. By setting within such a range, the flexural strength of the obtained sand mold can be more reliably increased.

[0063] The content ratio (solid content) of the fatty acid in the organic layer is not particularly limited as long as it is formulated to have the content shown above. Therefore, for example, it can be in the range of about 1 to 60% by mass, and can also be set to, for example, 5 to 50% by mass, or further 6 to 25% by mass.

[0064] (b) Heteropolyacid In the cast sand of the present invention, the heteropolyacid mainly functions as an acid catalyst (hereinafter also referred to as "acid hardener") for the curing of the coating binder used in the laminating step. By using this, a sand mold capable of exhibiting higher strength can be provided.

[0065] The heteropolyacid is a condensed acid containing two or more elements and oxygen, and in the present invention, various heteropolyacids can be used alone or in combination of two or more. In particular, in the present invention, heteropolyacids substantially free of sulfur element are preferred. In the present invention, "substantially free of" does not exclude even the case of being contained at the level of inevitable impurities. Therefore, the content of the sulfur element contained as an inevitable impurity in the commercially available heteropolyacid is acceptable. For example, if the content of the sulfur element is about 50 ppm by mass or less (particularly 0 to 10 ppm by mass), there is almost no problem due to the sulfur element, and it falls within the category of "substantially free of".

[0066] Also, the heteropolyacid is preferably water-soluble. Thereby, the heteropolyacid can suitably exist in the form of an aqueous solution in the above-mentioned aqueous wet layer. As a specific solubility, the solubility (27 ° C) in 100 g of water is preferably 100 to 1000 g / 100 g of water, and more preferably 300 to 900 g / 100 g of water. By using one having such a high solubility, the heteropolyacid can be contained at a higher concentration than the sulfonic acid-based curing agent (the above solubility is about 50 g / 100 g of water) at the same temperature, so that higher strength can be realized more quickly.

[0067] Furthermore, in the present invention, from the viewpoint of effectively functioning as an acid curing agent of the heteropolyacid, a heteropolyacid having an acid dissociation constant pKa (25 ° C) indicating an acid strength of 5 or less can be preferably used.

[0068] Examples of such heteropolyacids include at least one of phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, silicomolybdic acid, etc., and at least one of silicotungstic acid and phosphotungstic acid is particularly preferable. These heteropolyacids can be known or commercially available ones. Also, heteropolyacids obtained by known production methods can be used.

[0069] The content of the heteropolyacid component in the cast sand of the present invention is not limited, but is usually about 0.5 to 2.5 parts by mass, more preferably 0.6 to 2.0 parts by mass, and most preferably 1.0 to 1.5 parts by mass with respect to 100 parts by mass of sand grains. By setting within the above range, higher mold strength can be obtained.

[0070] The content ratio (solid content) of the heteropolyacid in the organic layer is not particularly limited as long as it is formulated so as to be the content (ratio to the sand grains) shown above, but it can usually be set within the range of about 10 to 99% by mass, and can also be within the range of about 10 to 80% by mass. Therefore, for example, it can be set to 30 to 60% by mass, or for example, it can be set to 40 to 99% by mass, or it can also be set to 50 to 95% by mass, and furthermore, it can be set to 55 to 93% by mass.

[0071] In order to efficiently and uniformly disperse the heteropolyacid with respect to the sand grains, if its form is a powder, its average primary particle diameter is usually about 0.6 to 30 μm, and particularly preferably 1 to 20 μm.

[0072] The heteropolyacid having such a particle size can be preferably obtained by, for example, a spray dryer.

[0073] The spraying method of the spray dryer is not particularly limited, and examples thereof include a four-fluid nozzle method and an atomizer disk method. In particular, in the present invention, in order to improve the dispersibility, it is preferable to adopt the four-fluid nozzle method from the viewpoint of obtaining finer-sized particles.

[0074] The inlet temperature of the spray dryer is not limited, but is usually about 100 to 200°C, and among them, it is preferably set to 150 to 180°C.

[0075] Also, the exhaust temperature of the spray dryer is usually about 50 to 150°C, and particularly preferably set to 80 to 120°C.

[0076] The pressure inside the tower of the spray dryer is not restrictive, but is usually about 0.1 to 1.0 MPa, and particularly preferably set to 0.3 to 0.8 MPa.

[0077] Furthermore, when the heteropolyacid is to be more homogeneously dispersed with respect to the sand grains, it is also possible to use, for example, a solution obtained by dissolving the heteropolyacid in at least one solvent of ethanol and water.

[0078] The content of the heteropolyacid contained in the solution can be appropriately set according to the heteropolyacid used, the type of the solvent, etc., but it is usually about 10 to 60% by mass, and particularly preferably about 30 to 50% by mass. Therefore, for example, it can also be 15 to 35% by mass.

[0079] (c) Other components In the organic layer, other components may be contained within a range that does not interfere with the effects of the present invention. For example, at least one or more of a solvent, a crosslinking agent, etc. can be contained.

[0080] As the solvent, for example, water can be preferably used. This is from the viewpoint that the boiling point is relatively high and it is easy to control the solubility of the organic layer composed of the furan resin precursor.

[0081] As the crosslinking agent, a silane coupling agent can be preferably used. Those known or commercially available can be used. In the present invention, since it can react with the organic layer and it is difficult to generate a precipitate derived from silane, at least one of aminopropylmethyldimethoxysilane and 3-methacryloxypropyltrimethoxysilane can be preferably used.

[0082] When using a crosslinking agent, its content ratio is not limited, but generally can be, for example, 0.002 to 0.5 parts by mass, particularly 0.001 to 0.5 parts by mass, based on 100 parts by mass of sand grains. Therefore, it can also be set to, for example, 0.02 to 0.5 parts by mass. By setting within such a range, the bonding strength between the organic layer and the sand grains can be further enhanced, and the adhesion between the coating binder and the organic layer can be further enhanced, resulting in the possibility of further increasing the mold strength. In this case, the content of the crosslinking agent in the organic layer may be in the above-mentioned content ratio, and can be, for example, about 1 to 50% by mass (particularly 20 to 40% by mass), but is not limited thereto.

[0083] 2. Method for manufacturing the casting sand of the present invention The method for manufacturing the casting sand of the present invention is not limited as long as it can form an organic layer on the sand grains. In the casting sands of the first embodiment and the second embodiment described above, it can be preferably manufactured by the following method.

[0084] (1) Manufacturing method of the first embodiment Regarding the casting sand according to the manufacturing method of the first embodiment, it is a method for manufacturing casting sand for three-dimensional laminated modeling, (1) A step of obtaining precursor particles coated with a coating layer containing the furan resin precursor or fatty acid on the surface of sand grains by mixing at least sand grains and a coating agent containing a furan resin precursor or a fatty acid having a melting point of 40 to 75°C at 100°C or lower (precursor particle preparation step), and (2) A step of obtaining composite particles in which the solid particles are supported on the coating layer on the surface of the precursor particles by mixing the precursor particles and solid particles of heteropolyacid at 100°C or lower (composite particle preparation step), It can be preferably manufactured by a method for manufacturing casting sand, which is characterized by including the above steps.

[0085] Precursor particle preparation step In the precursor particle preparation step, precursor particles coated with a coating layer containing the furan resin precursor or fatty acid on the surface of sand grains are obtained by mixing at least sand grains and a coating agent containing a furan resin precursor or a fatty acid having a melting point of 40 to 75°C at 100°C or lower.

[0086] For sand grains, furan resin precursors, fatty acids with a melting point of 40 to 75°C, etc., those similar to those described in the above-mentioned "1. Foundry sand for laminated sand molds" may be used.

[0087] As the coating agent, as described above, those containing (a1) a furan resin precursor or (a2) a fatty acid having a melting point of 40 to 75°C are used.

[0088] When using the furan resin precursor of the above (a1), the furan resin precursor is not particularly limited. However, in terms of being able to more reliably form a semi-cured state furan resin precursor, for example, as shown in the examples, a combination of furfuryl alcohol and a furan resin prepolymer (especially a urea-modified furan resin prepolymer) is preferably adopted.

[0089] The ratio of the two in this case may be the ratio described above. As the ratio in the coating agent, for example, furfuryl alcohol can be adjusted to be about 35 to 85% by mass, and the furan resin prepolymer can be adjusted to be about 15 to 65% by mass, but it is not limited thereto. Also, the content of the furan resin precursor in the coating agent is usually about 85 to 100% by mass, and can be particularly set to 90 to 98% by mass, but it is not limited thereto.

[0090] The mixing conditions are not limited as long as a coating layer can be formed on the surface of the sand grains with the coating agent. However, the temperature is preferably less than 100°C, particularly preferably 70°C or lower, and among them, 50 to 60°C is particularly preferred. Here, the temperature refers to the sand temperature (the same applies hereinafter), that is, it refers to the temperature of the material itself rather than the ambient temperature.

[0091] Further, the coating agent preferably contains a solvent (preferably water). By doing so, the organic layer can be made semi-cured more reliably. The content of the solvent can be appropriately set according to the type of the furan resin precursor or solvent used, but is usually about 1 to 10% by mass in the coating agent, and particularly preferably 3 to 7% by mass.

[0092] When using the fatty acid in (a2) above, it is desirable to preheat the sand grains before mixing the fatty acid. By doing so, the fatty acid particles can be dissolved and more uniformly coated on the sand grain surface. As specific examples of the fatty acid, those described above can be used.

[0093] The heating may be such that the sand temperature is 100°C or lower, particularly preferably 70°C or lower, and more preferably 50 to 60°C.

[0094] When dispersing the fatty acid efficiently and more homogeneously with respect to the sand grains, it is preferable to dissolve it using at least one of diethyl ether, benzene, ethanol, etc., which can be an organic solvent soluble in a fatty acid having a boiling point of less than 100°C, and among them, it is more preferable to use ethanol.

[0095] The content of the fatty acid in the solution can be appropriately set according to the type of the saturated fatty acid or solvent used, but is usually preferably 2 to 10% by mass, and particularly preferably 3 to 5% by mass.

[0096] In this step, the above-described coating agent is used, and the coating agent and the sand grains are mixed at 100°C or lower (preferably 60°C or lower, more preferably 40 to 50°C).

[0097] The mixing means is not limited, and for example, it can be mixed using a stirring device (such as a kneader, mixer, etc.) capable of temperature adjustment. These devices may use commercially available products.

[0098] In this way, precursor particles coated with a coating layer containing the furan resin precursor or fatty acid on the surface of the sand grains can be obtained.

[0099] Composite particle preparation step In the composite particle preparation step, the above-mentioned precursor particles and the powder of heteropolyacid are mixed at 100 °C or lower to obtain composite particles in which the solid particles are supported on the coating layer on the surface of the precursor particles.

[0100] Moreover, as the heteropolyacid, any of those described above may be used, and for example, at least one of silicotungstic acid and phosphotungstic acid can be preferably used.

[0101] As the solid particles of heteropolyacid, the powder of heteropolyacid described above can be used. Therefore, for example, powdery heteropolyacid having an average primary particle diameter of 0.6 to 30 μm (preferably 1 to 20 μm) can be preferably used.

[0102] Such solid particles of heteropolyacid and precursor particles are mixed at 100 °C or lower (preferably 80 °C or lower, more preferably 60 to 80 °C).

[0103] The mixing means is not limited, and for example, it can be mixed using a stirring device (such as a kneader, mixer, etc.) capable of temperature adjustment. These devices may use commercially available products.

[0104] In this way, composite particles in which the solid particles are supported on the coating layer on the surface of the precursor particles can be obtained. That is, as the composite particles, foundry sand can be obtained in which the organic layer is a carrier containing a furan resin precursor or a fatty acid having a melting point of 40 to 75 °C and solid particles of heteropolyacid are supported thereon.

[0105] In addition, when the obtained casting sand is not immediately used in the additive manufacturing process, it is usually desirable to store it in an environment controlled at a temperature of 15°C to 25°C and a humidity of 45% or less, particularly in an environment controlled at a temperature of 20°C to 25°C and a humidity of 40% or less. When storing outdoors, it is preferable to store it in a sealed state in a sealed container such as a drum can, for example.

[0106] (2) Manufacturing method of the second embodiment Regarding the casting sand according to the manufacturing method of the second embodiment, it is a method for manufacturing casting sand for three-dimensional additive manufacturing, (1) A step of obtaining precursor particles coated with an aqueous wet layer containing the aqueous solution on the surface of sand grains by mixing at least sand grains and an aqueous solution of heteropolyacid at 100°C or lower (precursor particle preparation step), (2) A step of obtaining composite particles in which the aqueous wet layer is covered with a hydrophobic layer containing the fatty acid by mixing the precursor particles and a furan resin precursor or a coating agent containing a fatty acid having a melting point of 40 to 75°C at 100°C or lower (composite particle preparation step), It can be preferably manufactured by a method for manufacturing casting sand, which is characterized by including the above steps.

[0107] Precursor particle preparation step In the precursor particle preparation step, precursor particles coated with an aqueous wet layer containing the aqueous solution are obtained by mixing at least sand grains and an aqueous solution of heteropolyacid at 100°C or lower.

[0108] As described above, for the heteropolyacid, for example, at least one of silicotungstic acid and phosphotungstic acid can be preferably used.

[0109] The aqueous solution of heteropolyacid can be prepared by dissolving the heteropolyacid in a solvent. As the solvent, a) water, b) a water-soluble organic solvent, or c) a mixture thereof can be preferably used. In the present invention, at least one of water and ethanol is more preferable.

[0110] The content of the heteropolyacid present in the solution is not particularly limited, but it is usually about 10 to 80% by mass, and particularly preferably 10 to 60% by mass.

[0111] As described above, the blending amount of the aqueous solution of the heteropolyacid is usually set so that the heteropolyacid is 0.5 to 2.5 parts by mass with respect to 100 parts by mass of the sand grains.

[0112] In particular, in the present invention, it is preferable to adjust the water content so that the mixture of the sand grains and the above aqueous solution becomes a wet mixture (kneaded product state, okara state). Therefore, a wet mixture can be suitably obtained by appropriately adjusting the concentration of the above aqueous solution. The adjustment of the water content can be carried out not only by the concentration of the aqueous solution of the heteropolyacid, but also by the temperature at the time of mixing (volatilization of water), the particle size distribution of the sand grains, the amount used, etc.

[0113] As described above, the mixing temperature may be 100°C or lower, but it is particularly preferably 60°C or lower, and more preferably 40 to 50°C.

[0114] Also, the mixing means is not limited, and for example, it can be mixed using a stirring device (kneader, mixer, etc.) capable of temperature control. Commercially available products of these devices may be used.

[0115] In this way, precursor particles coated with an aqueous wet layer containing the above aqueous solution on the surface of the sand grains can be obtained. The precursor particles having such an aqueous wet layer on the surface constitute the above wet mixture. And in the aqueous wet layer, the heteropolyacid exists in a solution (particularly an aqueous solution) state. In this regard, it is different from the first embodiment in which solid particles of the heteropolyacid are present.

[0116] Composite particle preparation step In the composite particle preparation step, the above precursor particles and a furan resin precursor or a coating agent containing a fatty acid having a melting point of 40 to 75°C are mixed at 100°C or lower to obtain composite particles in which the aqueous wet layer is covered with a hydrophobic layer containing the fatty acid.

[0117] As the coating agent containing a furan resin precursor or a fatty acid having a melting point of 40 to 75°C, for example, the same coating agent as that used in the method for producing casting sand of the first embodiment described above can be preferably used.

[0118] Such a coating agent and the precursor particles are mixed at 100°C or lower (preferably 70°C or lower, more preferably 50 to 60°C).

[0119] The mixing means is not limited, and for example, it can be mixed using a stirring device (such as a kneader, mixer, etc.) capable of temperature adjustment. These devices may use commercially available products.

[0120] In this way, composite particles in which the aqueous wet layer is covered with the hydrophobic layer containing the fatty acid can be obtained. That is, as the composite particles, a casting sand can be obtained in which the organic layer has an aqueous wet layer containing a heteropolyacid formed on the surface of the sand grains and a hydrophobic layer containing a furan resin precursor or a fatty acid having a melting point of 40 to 75°C, and the surface of the aqueous wet layer is covered with the hydrophobic layer.

[0121] 3. Kit for three-dimensional laminated modeling The present invention includes a kit for three-dimensional laminated modeling including the casting sand for three-dimensional laminated modeling of the present invention and a binder for coating. That is, before use, the casting sand of the present invention and the binder are stored separately, and it is provided as a two-component type kit in which both are mixed at the time of use.

[0122] The casting sand of the present invention, like that of the first embodiment, is a dry and flowing sand if the humidity in the sand grain gaps is low. Therefore, by filling it into a three-dimensional laminated modeling machine, it can be directly scattered (sprinkled). That is, it is also possible to let each particle of the casting sand fall naturally. On the other hand, if it is in an intermediate state with a high humidity in the sand grain gaps as in the second embodiment, although the filling property may be lower than that of dry sand, a practically usable strength can be exhibited.

[0123] The foundry sand of the present invention may contain additives other than the foundry sand of the present invention as long as the effects of the present invention are not impaired. For example, as described below, it is also possible to mix various additives such as anti-slip agents and thickeners with the foundry sand in advance and provide them.

[0124] The binder for coating is a binder that is sprayed onto the formed foundry sand layer during three-dimensional laminated molding. In particular, when manufacturing a sand mold using a three-dimensional laminated molding machine or the like, in order to stably discharge the binder for coating from the print head, the viscosity (25 ° C) is preferably 1 to 15 mPa·s.

[0125] The type of the binder for coating is not particularly limited, and any binder that can be used in a known or commercially available three-dimensional laminated molding machine may be used. In particular, in the present invention, it is preferable to use a binder for coating containing a furan resin precursor. The content of the furan resin precursor can be, for example, 80 to 100% by mass in the binder, and particularly 90 to 100% by mass, but is not limited thereto.

[0126] The furan resin precursor is not limited as long as it can form a furan resin by condensation polymerization or the like. Examples thereof include furfuryl alcohol and furan resin prepolymers. In particular, for the reasons of suppressing the heat of reaction and reducing the viscosity of the resin, it is desirable to use furfuryl alcohol and a furan resin prepolymer in combination.

[0127] Examples of the furan resin prepolymer include polymers of furfuryl alcohol alone, copolymers of furfuryl alcohol and aldehyde compounds, copolymers of furfuryl alcohol, urea and aldehyde compounds (urea-modified furan resin prepolymers), and copolymers of furfuryl alcohol and furfural. These can be used alone or in combination of two or more.

[0128] In the present invention, a copolymer of furfuryl alcohol, urea, and an aldehyde compound (urea-modified furan resin prepolymer) is particularly preferable because it is easy to increase the strength. Examples of the aldehyde compound include formaldehyde, acetaldehyde, glyoxal, furfural, and the like. In the present invention, formaldehyde is particularly preferable.

[0129] Within a range that does not interfere with the effects of the present invention, other components may be contained in the binder for coating. For example, additives such as solvents, crosslinking agents, and curing accelerators can be contained as necessary. In particular, as the solvent, water is preferable in the present invention because the reaction rate becomes moderate and the final mold strength is easily increased.

[0130] Examples of the curing accelerator include at least one of resorcin, cresol, hydroquinone, phloroglucinol, methylene bisphenol, bis(hydroxymethyl)furan, and the like. Among these, resorcin is particularly preferable because the reaction rate is fast and high strength of the mold is easily obtained.

[0131] The addition amount of the curing accelerator is appropriately adjusted as necessary in view of the amount of generated reaction water and the like, and thus it is not an essential component and may not be particularly contained.

[0132] In addition, since the casting sand, which is the other material of the kit, has an organic layer containing an acid component, the binder for coating can strongly bond the casting sands together even without a silane coupling agent. Therefore, the content of the silane coupling agent in the binder for coating is usually about 0 to 1% by mass, preferably 0 to 0.1% by mass. Therefore, a composition not containing a silane coupling agent may also be used. For example, it can also be set to 0.05 to 0.15% by mass. By setting the content of the silane coupling agent to a small amount or 0% by mass in this way, it becomes possible to stably store the binder for coating for a longer period.

[0133] Furthermore, an amine compound can be added to the binder for coating, if necessary. By adding the amine compound, the change in viscosity of the furan resin precursor over time can be effectively suppressed. From this perspective, as the amine compound, an alkylamine having 10 or less carbon atoms is preferable, and butylamine is more preferable.

[0134] The addition amount of the amine compound is not limited, but if it is excessive, there are problems such as a slow curing rate and the induction of gas defects due to nitrogen. Therefore, the content of the amine compound is desirably about 0.001 to 1% by mass in the binder for coating, more desirably 0.001 to 0.5% by mass, still more desirably 0.005 to 0.1% by mass, and most desirably 0.01 to 0.05% by mass. Therefore, for example, it can also be set within the range of 0 to 0.5% by mass.

[0135] Regarding the usage amount of the binder for coating, due to the mechanical settings of the printer head, the upper limit value that can be coated is preferably 3 parts by mass or less with respect to 100 parts by mass of sand. Usually, it is in the range of about 0.5 to 3 parts by mass with respect to 100 parts by mass of the casting sand of the present invention, and particularly preferably 1 to 3 parts by mass. If the binder for coating is too little, the strength of the sand mold may not be obtained. Therefore, as long as the amounts of the casting sand and the binder are in the above ratio during use, it is not necessarily required that the kit of the present invention be made into a kit in the above ratio.

[0136] In the present invention, the type of the furan resin precursor contained in the binder for coating and the type of the furan resin precursor contained in the organic layer of the casting sand of the present invention may be the same as each other or different from each other. Therefore, for example, when the organic layer of the casting sand of the present invention contains a combination of furfuryl alcohol and a furan resin prepolymer (particularly a urea-modified furan resin prepolymer), a binder for coating containing a combination of furfuryl alcohol and a furan resin prepolymer (particularly a urea-modified furan resin prepolymer) can be employed.

[0137] In this case, particularly when the same types are adopted for each other, the compatibility between the organic layer of the foundry sand and the binder for coating becomes better, and higher mold strength can be achieved. For example, in the foundry sand of the present invention in which the organic layer contains a combination of furfuryl alcohol and a furan resin prepolymer (particularly a urea-modified furan resin prepolymer), it can also be used as a foundry sand suitable for a combination with a binder for coating containing furfuryl alcohol and a furan resin prepolymer as the binder for coating used during stereolithography.

[0138] However, even when the same types are adopted for each other, it is not always necessary to make them completely identical including, for example, the composition ratio, additives, etc. While considering the balance between the casting strength and the curing time, etc., it is possible to finely adjust the blending ratio of furfuryl alcohol, furan resin polymer, etc., and the type of additives, etc., taking into account the characteristics of the three-dimensional stereolithography machine to be used.

[0139] 4. Use of Foundry Sand for Three-Dimensional Stereolithography The foundry sand of the present invention can be used for lamination in the same manner as known foundry sand. More specifically, in a method for manufacturing a sand mold by a three-dimensional stereolithography method including a step of forming a layer containing the foundry sand (layer forming step) and a step of solidifying a predetermined region of the layer by adding a binder for coating to the region (binder for coating addition step), the foundry sand of the present invention can be preferably used as the foundry sand. As described above, by supplying the foundry sand of the present invention to a known or commercially available three-dimensional stereolithography machine, a sand mold having a desired shape can be manufactured. In other words, the foundry sand of the present invention can be preferably used as the foundry sand used in a three-dimensional stereolithography machine.

[0140] As such a three-dimensional laminating machine, for example, a machine having a unit, a casting sand supply unit, a binder supply unit for coating, and an operation unit can be used to produce a sand mold from 3D-CAD data. The casting sand supply unit is a unit that supplies casting sand to the unit, and includes a casting sand tank for storing the casting sand, a recoater that can discharge the casting sand while moving horizontally, and the like. The binder supply unit for coating includes a print head that discharges the binder for coating to the unit. Such a device itself can use a known or commercially available one.

[0141] When manufacturing a sand mold by a three-dimensional laminating method, as described above, a laminating method including a step of forming a layer containing casting sand (layer forming step) and a step of solidifying a predetermined region of the layer by adding a binder for coating to the region (binder addition step for coating) can be adopted. At this time, a desired sand mold can be obtained because the hardener contained in the organic layer of the casting sand whose surface of the sand grains is a furan resin contributes to the solidification of both the organic layer and the binder for coating.

[0142] Layer forming step In the layer forming step, a layer containing casting sand is formed. More specifically, a layer containing casting sand can be formed by sprinkling the casting sand from above. Since the casting sand of the present invention is basically in a dry sand state with a smooth texture, it can also be smoothly dropped naturally (sprayed). Even when the humidity of the sand grain gaps is high, when using the three-dimensional laminating machine as described above, the layer can be surely formed by discharging the casting sand from a horizontally moving recoater onto a flat surface.

[0143] Further, in the layer forming step, within a range that does not prevent smooth layer formation, components other than casting sand may be included in the layer. As such components, components added to known casting sand can also be adopted.

[0144] In the conventional laminated manufacturing method (two-component mixing process of wet sand, hardener, and binder resin for coating), when artificial sand produced by a melting method or the like is used as sand grains for casting sand, due to the influence of its surface smoothness and roundness, when a liquid agent is added to the casting sand, the casting sands cause a liquid crosslinking phenomenon (aggregation), the fluidity of the sand, which is important in the laminated manufacturing method, is impaired, and it becomes difficult to use small-sized sand grains. For this reason, a method has been proposed in which a drying process is added to make it in a dry sand state and improve the fluidity, but the sand grains that can be used are limited to sintered artificial sand. On the other hand, in the casting sand of the present invention, when a fatty acid such as linoleic acid is added as an anti-slip agent to the organic layer, or in the case of casting sand in a state where the humidity between sand grains is high (that is, a so-called intermediate state), regardless of the sand type, particle size, etc., stable laminating properties can be obtained more reliably. Thereby, even when using melting method artificial sand with high smoothness and roundness as sand grains, for example, it is possible to prevent the casting sand layer of the present invention from collapsing in a shaping box (Job box) in a three-dimensional laminating machine.

[0145] The thickness of the layer depends on the particle size of the casting sand, the desired sand mold shape, etc., but is usually about 100 to 400 μm, and particularly preferably 200 to 300 μm. When the layer formation process is repeated, the layer thicknesses formed in each layer formation process may be the same as each other or different from each other.

[0146] Binder addition step for coating The predetermined region is solidified by adding (spraying) a binder for coating to the predetermined region of the layer. Although a layer containing casting sand is formed as a single layer by the layer formation process, a binder for coating is added to the region based on the data of the cross-sectional shape of the target sand mold. For example, when using the three-dimensional laminating machine as described above, the predetermined region can be solidified by spraying a binder for coating onto the layer from a horizontally moving print head (nozzle). As the binder for coating and the like, those described in, for example, the above-mentioned "3. Three-dimensional laminating kit" can also be used.

[0147] After the repetition of a series of steps consisting of a layer forming step and a step of adding a binder for coating is completed, a sand mold having a predetermined shape can be obtained by removing the portions where the binder for coating has not been added.

[0148] The sand mold obtained as described above can be aged as necessary. Thereby, the curing of the resin component can be promoted, and a sand mold having higher strength can be obtained. The aging conditions are, for example, a temperature of 15 to 25°C and a humidity of 45% or less, and particularly, the temperature can be 20 to 25°C and the humidity can be 40% or less, but it is not limited thereto. For example, the temperature can be 20 to 25°C and the humidity can be 30 to 45%. Also, the aging time can be, for example, about 1 to 48 hours, but it is not limited thereto.

[0149] Furthermore, a step of applying a mold coating agent to the obtained sand mold can be carried out as necessary. The method for applying the mold coating agent to the sand mold is not particularly limited, and examples include brush coating, dipping, etc. There is no problem with brush coating, but dipping is preferably performed when it is desired to apply the mold coating agent more uniformly to the entire sand mold, but it is not limited thereto. In this case, either an aqueous mold coating agent or a non-aqueous mold coating agent can be used as the mold coating agent, but it is desirable to use an aqueous mold coating agent from the viewpoint of safety and the like.

[0150] However, dipping an aqueous mold coating agent is not recommended for a sand mold made from conventional casting sand for laminated molding. This is because in the sand mold immediately after lamination, the furan resin precursor has not been sufficiently polymerized. In addition, dipping the sand mold into the aqueous mold coating agent causes the moisture contained in the aqueous mold coating agent to further penetrate into the mold, resulting in a decrease in the strength of the sand mold or deformation of the sand mold during drying of the aqueous mold coating agent.

[0151] From this perspective as well, in the present invention, as will also be shown hereinafter, prior to the application of the aqueous coating agent, it is desirable to perform a heat treatment on the above sand mold in advance after the above aging or in place of the above aging to promote the curing reaction of the moisture and unreacted furan resin precursor contained inside the sand mold and approach complete curing. In this case, the heat treatment temperature is desirably, for example, about 40 to 250 °C, particularly preferably 50 to 180 °C, and most preferably 50 to 100 °C, but is not limited thereto. The heat treatment time is also, for example, 10 minutes to 2 hours, and particularly preferably 10 minutes to 1 hour, but is not limited thereto.

[0152] In the casting sand of the present invention, the reaction water generated when the furan resin precursor polymerizes is controlled (suppression of internal curing defects). In addition, by performing a heat treatment (preliminary drying) before applying the aqueous coating agent, the curing reaction of the furan resin can be promoted and brought closer to complete curing. As a result, even when an aqueous coating agent is applied (dipping, etc.) to the sand mold, the flexural strength does not decrease, and during the drying of the aqueous coating agent, it is possible to effectively prevent deformation that may occur in the sand mold.

[0153] In the sand mold thus obtained using suitable casting sand in this way, high strength and high design reproducibility can be realized. In addition, it is excellent in mass productivity, and usually it is possible to take out the sand mold in about 3 hours or less, and if it is fast, in about 1 hour. Therefore, the laminated manufacturing method can be widely applied to the manufacture of casting products that require mass productivity.

[0154] 5. Sand Mold The present invention includes a sand mold (particularly a sand mold for casting iron-based materials) containing the casting sand for three-dimensional laminated manufacturing of the present invention. The sand mold of the present invention is configured by the individual particles of the casting sand of the present invention adhering and joining to each other, and can exhibit high strength. In particular, the present invention also includes a sand mold containing an aqueous coating agent (particularly a sand mold for casting iron-based materials).

[0155] The sand mold of the present invention can be used as a casting sand mold for casting substantially any material (especially metals), and is particularly preferably used for casting iron-based materials. Generally, when casting iron-based materials, if a sulfur component is contained in the sand mold (or the molding sand that constitutes it), sulfur infiltration into the casting will occur, causing poor spheroidization (metallographic structure) of graphite, which affects the quality of the casting and may lead to a decrease in the strength of the casting. In contrast, since the molding sand that constitutes the sand mold of the present invention substantially does not contain a sulfur component, problems caused by the sulfur component can be avoided.

[0156] The sand mold of the present invention can be manufactured by the above-described three-dimensional laminating method. In particular, the sand mold can be preferably manufactured by the following method.

[0157] That is, it is a method for manufacturing a sand mold using the casting sand for three-dimensional laminating of the present invention, (1) A step of obtaining a molded body by repeatedly performing, in order, a step of forming a layer containing the casting sand and a step of solidifying a predetermined region of the layer by adding a coating binder to the region (laminating step), and (2) A step of obtaining a sand mold by heat-treating the molded body not containing an aqueous coating agent in the air or an inert gas atmosphere at 40 to 250°C (heat-treatment step) It can be preferably manufactured by a method for manufacturing a sand mold, characterized by including the above.

[0158] Laminating step In the laminating step, a molded body is obtained by repeatedly performing, in order, a step of forming a layer containing the casting sand and a step of solidifying a predetermined region of the layer by adding a coating binder to the region.

[0159] The laminating step may be carried out in the same manner as the three-dimensional laminating method shown in the above "4. Use of casting sand for three-dimensional laminating".

[0160] Heat-treatment step In the heat treatment step, the mold is obtained by heat-treating the molded body containing no aqueous coating agent at 40 to 250°C in the air or an inert gas atmosphere. That is, heat treatment is performed prior to adding (coating) the aqueous coating agent to the molded body. Thereby, deformation of the mold that may occur when the aqueous coating agent is applied to the mold can be more reliably suppressed.

[0161] The heat treatment step may be carried out in the same manner as the heat treatment shown in the above-mentioned "4. Use of casting sand for 3D laminated molding".

[0162] Therefore, the heat treatment temperature is usually 40 to 250°C, particularly preferably 50 to 180°C, and most preferably 50 to 100°C, but is not limited thereto. The heat treatment time can usually be about 10 minutes to 2 hours, and more preferably 10 minutes to 1 hour, but is not limited thereto.

[0163] The heating atmosphere may be the air (in the air) or an inert gas atmosphere. As the inert gas, without limitation, any of nitrogen gas, argon gas, helium gas, etc. can be used.

[0164] Generally, when manufacturing an iron-based molded body by putting an iron-based material into a mold and casting, an aqueous coating agent (particularly an aqueous dispersion of an inorganic material) is applied to at least the region where the mold contacts the iron-based material (molten metal). In a conventional mold, when an aqueous coating agent is applied, phenomena such as deformation or cracking of the mold may occur. In contrast, since the mold of the present invention uses a heteropolyacid as an acid curing agent, the acid curing agent is effectively dispersed (penetrated) to the central part of the intergranular bridge forming the cured body of the furan resin precursor (having higher solubility in water than sulfonic acid), so that high strength can be obtained.

[0165] Moreover, by performing the heat treatment as described above, the furan resin precursor can be more surely brought closer to complete curing. Moreover, as described above, since the heteropolyacid, which is an acid curing agent, is uniformly dispersed, three-dimensional polymerization of the furan resin precursor can be further promoted by heat treatment, and as a result, it can effectively contribute to preventing deformation (such as deformation of the sand mold and generation of cracks).

[0166] The sand mold thus obtained can be used as a casting sand mold for casting various materials (especially metals) as described above, and can be particularly preferably used for casting iron-based materials.

[0167] When manufacturing an iron-based molded product by casting an iron-based material using the sand mold of the present invention, for example, when manufacturing an iron-based molded product, a production method including: a) a step of applying an aqueous coating agent to the sand mold of the present invention; and b) a step of pouring a molten iron-based material into the sand mold can be preferably used.

[0168] The step a) can be carried out in the same manner as the above-described coating step. However, when the aqueous coating agent has been previously applied to the sand mold, the step a) can be omitted. Therefore, in this case, an iron-based molded product can be preferably manufactured by a method including a step of pouring a molten iron-based material into the sand mold of the present invention containing the aqueous coating agent.

[0169] As the aqueous coating agent, a coating agent in which an inorganic component is dispersed in an aqueous solvent can be preferably used. As the inorganic component, for example, an aqueous coating agent containing at least one oxide such as silica, alumina, magnesia, and zirconia can be preferably used. These can also be known or commercially available products. Therefore, various additives (dispersants, antifoaming agents, thickeners, etc.) contained in commercially available products may be contained in the aqueous coating agent as long as the effects of the present invention are not impaired.

[0170] As the aqueous solvent, (a) water, (b) a water-soluble organic solvent, or (c) a mixture (aqueous solution) of water and a water-soluble organic solvent can be used. As the water-soluble organic solvent, although not limited, for example, at least one of alcohols such as methanol, ethanol, and isopropyl alcohol can be preferably used.

[0171] The method of applying the aqueous coating agent is not limited, and depending on the size of the sand mold, etc., for example, various coating methods such as dipping, spraying, brushing, and rolling can all be adopted. The application to the sand mold may be, for example, coating the aqueous coating agent on the area of the sand mold surface that is at least in contact with the molten metal (molten metal), but the entire sand mold may also be coated.

[0172] Note that the coating process may be carried out continuously after the heat treatment process of the above-mentioned method for manufacturing the sand mold, but in the sand mold that has undergone the heat treatment process, the coating process may not be carried out immediately, and it can also be carried out immediately before its use (casting). For example, after manufacturing a sand mold that has undergone a heat treatment process and after a certain period has elapsed, when using the sand mold (more specifically, before pouring the molten metal into the sand mold), an aqueous coating agent can be applied to the sand mold.

[0173] After applying the aqueous coating agent to the sand mold surface, a drying process may be carried out. The drying can be either natural drying or heat drying, but in the case of heat drying, it is usually carried out at a temperature within the range of 50 to 180°C, and more preferably 80 to 120°C is desirable. The heat drying time can be appropriately changed depending on the heating temperature, etc., but it can usually be appropriately determined within the range of about 30 to 120 minutes.

[0174] Next, in the step of b) above, the molten iron-based material is poured into the sand mold. More specifically, the molten iron-based material is poured into the sand mold so as to contact the surface of the sand mold on which the coating film formed by the aqueous coating agent of the sand mold is formed. The iron-based material may be any material containing iron as the main component (especially an iron content of 50% by mass or more), and an iron-based material having a composition corresponding to various iron-based products can be used.

[0175] After pouring the molten iron-based material and completing the casting, the sand mold can be broken according to a known method to take out the iron-based formed body.

Example

[0176] Examples and comparative examples are shown below to more specifically explain the features of this study. However, the scope of the present invention is not limited to the examples. Note that “%” indicating the content of the composition in each table all means “mass %”.

[0177] Example 1 300 g of new sand of mullite-based fused artificial sand with AFS65 (AlSand #650 manufactured by Ito Kiko Co., Ltd., angle of repose 25°) (ARS fused new sand) as sand grains, palmitic acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) as a coating agent, and ketatungstic acid (manufactured by Nippon Inorganic Chemical Industry Co., Ltd., D50 = 1.0 μm) which is an acid hardening agent were prepared. While heating the sand, 0.2 part by mass of palmitic acid was added to 100 parts by mass of the artificial sand in a state where the sand temperature of the artificial sand reached 50°C, and the mixture was stirred and mixed for 60 seconds. The sand temperature was 70°C. Next, 1.0 part by mass of ketatungstic acid was added to the obtained mixture with respect to 100 parts by mass of the artificial sand, and the mixture was stirred and mixed for 120 seconds to obtain dry-state casting sand.

[0178] Example 2 Dry-state casting sand same as that in Example 1 was prepared.

[0179] Example 3 The sand grains were changed to 300 g of new sand of mullite-based fired artificial sand with AFS64 (Cerabeads X#650 manufactured by Itochu Ceramics Co., Ltd., angle of repose 28°) (CBX sintered new sand), palmitic acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.), and ketatungstic acid (manufactured by Nippon Inorganic Chemical Industry Co., Ltd., D50 = 1.0 μm) which is an acid hardening agent were prepared. While heating the sand, 0.1 part by mass of palmitic acid was added to 100 parts by mass of the artificial sand in a state where the sand temperature of the artificial sand reached 50°C, and the mixture was stirred and mixed for 60 seconds. The sand temperature was 70°C. Next, 1.0 part by mass of ketatungstic acid was added to the obtained mixture with respect to 100 parts by mass of the artificial sand, and the mixture was stirred and mixed for 120 seconds to obtain dry-state casting sand.

[0180] Example 4 The sand grains were changed to 300 g of new sand of AFS78 mullite-based fused artificial sand (Espal #75L manufactured by Yamakawa Sangyo Co., Ltd., angle of repose 24°) (EP fused new sand), palmitic acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.), and potassium tungstate (manufactured by Nippon Inorganic Chemical Industry Co., Ltd., D50 = 1.0 μm) as an acid hardener were prepared. While heating the sand, 0.1 part by mass of palmitic acid was added to 100 parts by mass of the artificial sand in a state where the sand temperature of the artificial sand reached 50°C, and they were stirred and mixed for 60 seconds. The sand temperature was 67°C. Next, 1.0 part by mass of potassium tungstate was added to the obtained mixture with respect to 100 parts by mass of the artificial sand, and they were stirred and mixed for 120 seconds to obtain dry-state casting sand.

[0181] Example 5 The sand grains were changed to 300 g of new sand of AFS96 natural silica sand (Albany #90 manufactured by Tsuchu Co., Ltd., angle of repose 36°) (ALB silica new sand), palmitic acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.), and potassium tungstate (manufactured by Nippon Inorganic Chemical Industry Co., Ltd., D50 = 1.0 μm) as an acid hardener were prepared. While heating the sand, 0.2 part by mass of palmitic acid was added to 100 parts by mass of the silica sand in a state where the sand temperature of the silica sand reached 50°C, and they were stirred and mixed for 60 seconds. The sand temperature was 70°C. Next, 1.0 part by mass of potassium tungstate was added to the obtained mixture with respect to 100 parts by mass of the silica sand, and they were stirred and mixed for 120 seconds to obtain dry-state casting sand.

[0182] Example 6 The sand was changed to a mixed sand obtained by stirring and mixing AFS56 roasted and recycled sand (recycled sand No. 6 manufactured by Tochu Co., with an angle of repose of 34°) (roasted and recycled sand) and natural silica sand of AFS96 new sand in a mass ratio of 7:3. Palmitic acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) and potassium tungstate as an acid hardener (manufactured by Nippon Inorganic Chemical Industry Co., Ltd., D50 = 1.0 μm) were prepared. While heating the sand, when the sand temperature of the above mixed sand reached 50°C, 0.2 parts by mass of palmitic acid was added to 100 parts by mass of the mixed sand and stirred and mixed for 60 seconds. The sand temperature was 70°C. Next, 1.0 part by mass of potassium tungstate was added to the obtained mixture per 100 parts by mass of the mixed sand, and stirred and mixed for 120 seconds to obtain dry-state casting sand.

[0183] Example 7 Casting sand was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 4 were used. In particular, the following changes were made to Example 1. 1.1 parts by mass of palmitic acid was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 75°C. Next, 1.5 parts by mass of potassium tungstate was added to the obtained mixture per 100 parts by mass of artificial sand, and stirred and mixed for 120 seconds to obtain dry-state casting sand.

[0184] Example 8 Casting sand was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 4 were used. In particular, the following changes were made to Example 1. 0.02 parts by mass of palmitic acid was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 70°C. Next, 1.5 parts by mass of potassium tungstate was added to the obtained mixture per 100 parts by mass of artificial sand, and stirred and mixed for 120 seconds to obtain dry-state casting sand.

[0185] Example 9 Foundry sand was prepared in the same manner as in Example 3, except that the composition and conditions shown in Table 4 were used. In particular, the following changes were made to Example 3. As a coating agent, 0.1 part by mass of stearic acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 70°C. Next, 1.0 part by mass of potassium tungstate was added to the obtained mixture per 100 parts by mass of artificial sand, and the mixture was stirred and mixed for 120 seconds to obtain dry-state foundry sand.

[0186] Example 10 Foundry sand was prepared in the same manner as in Example 3, except that the composition and conditions shown in Table 4 were used. In particular, the following changes were made to Example 3. As a coating agent, 0.1 part by mass of lauric acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 69°C. Next, 1.0 part by mass of potassium tungstate was added to the obtained mixture per 100 parts by mass of artificial sand, and the mixture was stirred and mixed for 120 seconds to obtain dry-state foundry sand.

[0187] Example 11 Foundry sand was prepared in the same manner as in Example 3, except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 3. As a coating agent, 0.1 part by mass of the furan resin composition "Constitution 1" in Table 1 was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 60°C. Next, 1.0 part by mass of potassium tungstate was added to the obtained mixture per 100 parts by mass of artificial sand, and the mixture was stirred and mixed for 120 seconds to obtain dry-state foundry sand.

[0188]

Table 1

[0189] Example 12 Foundry sand was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 1. 0.2 parts by mass of palmitic acid was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 66 °C. Next, a solution prepared by mixing 1.0 part by mass of phosphotungstic acid (manufactured by Nippon Inorganic Chemical Industry Co., Ltd., D50 = 55 μm) as an acid hardener and 1.0 part by mass of ethanol as a solvent with respect to 100 parts by mass of artificial sand was added to the obtained mixture, and stirred and mixed for 120 seconds to obtain dry-state foundry sand.

[0190] Example 13 Foundry sand was prepared in the same manner as in Example 3, except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 3. 0.1 part by mass of palmitic acid was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 70 °C. Next, 1.0 part by mass of silicotungstic acid (manufactured by Nippon Inorganic Chemical Industry Co., Ltd., D50 = 20 μm) as a hardener was added to 100 parts by mass of artificial sand, and stirred and mixed for 120 seconds to obtain dry-state foundry sand.

[0191] Example 14 Foundry sand was prepared in the same manner as in Example 3, except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 3. 0.1 part by mass of palmitic acid was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 80 °C. Next, a solution prepared by mixing 1.0 part by mass of silicotungstic acid as an acid hardener and 1.0 part by mass of ethanol as a solvent with respect to 100 parts by mass of artificial sand was added to the obtained mixture, and stirred and mixed for 120 seconds to obtain dry-state foundry sand.

[0192] Example 15 Molding sand was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 1. 0.1 part by mass of palmitic acid was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 76°C. Next, 2.0 parts by mass of potassium tungstate was added to the obtained mixture per 100 parts by mass of artificial sand, and stirred and mixed for 120 seconds to obtain dry-state molding sand.

[0193] Example 16 Molding sand was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 1. 0.1 part by mass of palmitic acid was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 70°C. Next, 0.5 part by mass of potassium tungstate was added to the obtained mixture per 100 parts by mass of artificial sand, and stirred and mixed for 120 seconds to obtain dry-state molding sand.

[0194] Example 17 The sand grains were changed to 300 g of new sand of AFS64 mullite-based fired artificial sand (Celabeads X#650 manufactured by Itochu Ceramics Co., Ltd., angle of repose 28°) (CBX sintered new sand), and as additives, the silane coupling agent "Composition 2" in Table 2, palmitic acid (manufactured by Fujifilm Wako Pure Chemical Corporation), and potassium tungstate (manufactured by Nippon Inorganic Chemical Industry Co., Ltd., D50 = 1.0 μm), which is an acid curing agent, were prepared. While heating the sand, when the sand temperature of the above artificial sand reached 50°C, 0.5 part by mass of the silane coupling agent of Composition 2 was added to 100 parts by mass of the above artificial sand and stirred and mixed for 60 seconds. The sand temperature was 66°C. Next, 0.1 part by mass of palmitic acid was added to the obtained mixture per 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 77°C. Finally, 1.0 part by mass of potassium tungstate was added to the obtained mixture per 100 parts by mass of artificial sand and stirred and mixed for 120 seconds to obtain dry-state molding sand.

[0195]

Table 2

[0196] Example 18 Molding sand was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 1. As the coating agent, 2.1 parts by mass of the furan resin composition "Constitution 1" in Table 1 was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 74°C. Next, 1.5 parts by mass of potassium tungstate was added to 100 parts by mass of artificial sand to the obtained mixture, and stirred and mixed for 120 seconds to obtain dry-state molding sand.

[0197] Example 19 Molding sand was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 1. As the coating agent, 0.03 parts by mass of the furan resin composition "Constitution 1" in Table 1 was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 66°C. Next, 1.5 parts by mass of potassium tungstate was added to 100 parts by mass of artificial sand to the obtained mixture, and stirred and mixed for 120 seconds to obtain dry-state molding sand.

[0198] Example 20 Molding sand was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 1. As the coating agent, 0.2 parts by mass of the furan resin composition "Constitution 1" in Table 1 was added to 100 parts by mass of artificial sand and stirred and mixed for 60 seconds. The sand temperature was 60°C. Next, 0.8 parts by mass of potassium tungstate was added to 100 parts by mass of artificial sand to the obtained mixture, and stirred and mixed for 120 seconds to obtain dry-state molding sand.

[0199] Example 21 The sand was changed to 300 g of new sand of AFS64 mullite-based fired artificial sand (Cerabeads X#650 manufactured by Itochu Ceramics Co., Ltd., angle of repose 28°) (CBX sintered new sand), palmitic acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.), and ketatanic acid (manufactured by Nippon Inorganic Chemical Industry Co., Ltd., D50 = 1.0 μm), which is an acid hardening agent, were prepared. While heating the sand, an aqueous solution in which 1.0 part by mass of ketatanic acid and 3.3 parts by mass of water as a solvent were mixed was added to 100 parts by mass of the artificial sand in a state where the sand temperature of the artificial sand reached 40°C, and the mixture was stirred and mixed for 90 seconds. The sand temperature was 65°C. Next, 0.1 part by mass of palmitic acid was added to 100 parts by mass of the artificial sand to the obtained mixture, and the mixture was stirred and mixed for 60 seconds to obtain intermediate foundry sand.

[0200] Comparative Example 1 300 g of new sand of AFS65 mullite-based fused artificial sand (Alsand #650 manufactured by Ito Machine Works, Ltd., angle of repose 25°) and ketatanic acid (manufactured by Nippon Inorganic Chemical Industry Co., Ltd., D50 = 1.0 μm), which is a hardening agent, were prepared. The sand was not heated. 0.4 part by mass of ketatanic acid was added to 100 parts by mass of the artificial sand in a state where the sand temperature of the artificial sand was 25°C, and the mixture was stirred and mixed for 120 seconds to obtain dry-state foundry sand.

[0201] Comparative Example 2 Foundry sand was prepared in the same manner as in Comparative Example 1, except that the composition and conditions shown in Table 6 were used. In particular, the following changes were made to Comparative Example 1. Ketatanic acid, which is an acid hardening agent, was prepared. The sand was not heated. 1.0 part by mass of ketatanic acid was added to 100 parts by mass of the artificial sand in a state where the sand temperature of the artificial sand was 25°C, and the mixture was stirred and mixed for 120 seconds to obtain dry-state foundry sand.

[0202] Comparative Example 3 Foundry sand was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 6 were used. In particular, the following changes were made to Example 1. 1.2 parts by mass of palmitic acid was added to 100 parts by mass of artificial sand and stirred for 60 seconds. The sand temperature was 70 °C. Next, 1.5 parts by mass of potassium tungstate was added to 100 parts by mass of artificial sand, and the mixture was stirred for 120 seconds to obtain dry-state foundry sand.

[0203] Comparative Example 4 Foundry sand was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 6 were used. In particular, the following changes were made to Example 1. 0.01 parts by mass of palmitic acid was added to 100 parts by mass of artificial sand and stirred for 60 seconds. The sand temperature was 75 °C. Next, 1.5 parts by mass of potassium tungstate was added to 100 parts by mass of artificial sand, and the mixture was stirred for 120 seconds to obtain dry-state foundry sand.

[0204] Comparative Example 5 Foundry sand was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 6 were used. In particular, the following changes were made to Example 1. 0.1 parts by mass of palmitic acid was added to 100 parts by mass of artificial sand and stirred for 60 seconds. The sand temperature was 70 °C. Next, 3.0 parts by mass of potassium tungstate was added to 100 parts by mass of artificial sand, and the mixture was stirred for 120 seconds to obtain dry-state foundry sand.

[0205] Comparative Example 6 Foundry sand was prepared in the same manner as in Example 1, except that the composition and conditions shown in Table 6 were used. In particular, the following changes were made to Example 1. 0.1 parts by mass of palmitic acid was added to 100 parts by mass of artificial sand and stirred for 60 seconds. The sand temperature was 72 °C. Next, 0.4 parts by mass of potassium tungstate was added to 100 parts by mass of artificial sand, and the mixture was stirred for 120 seconds to obtain dry-state foundry sand.

[0206] Comparative Example 7 Molding sand was prepared in the same manner as in Example 11, except for the composition and conditions shown in Table 6. In particular, the following changes were made to Example 11. To 100 parts by mass of artificial sand, 2.2 parts by mass of the furan resin composition of "Configuration 1" was added and stirred for 60 seconds. The sand temperature was 64°C. Next, 1.5 parts by mass of potassium tungstate was added to 100 parts by mass of artificial sand, and the mixture was stirred and mixed for 120 seconds to obtain dry-state molding sand.

[0207] Comparative Example 8 Molding sand was prepared in the same manner as in Example 11, except for the composition and conditions shown in Table 6. In particular, the following changes were made to Example 11. To 100 parts by mass of artificial sand, 0.02 parts by mass of the furan resin composition of "Configuration 1" was added and stirred for 60 seconds. The sand temperature was 70°C. Next, 1.5 parts by mass of potassium tungstate was added to 100 parts by mass of artificial sand, and the mixture was stirred and mixed for 120 seconds to obtain dry-state molding sand.

[0208] Comparative Example 9 The sand grains were changed to 300 g of new sand of AFS64 mullite-based fired artificial sand (Celabeads X#650 manufactured by Itochu Ceramics Co., Ltd., angle of repose 28°) (CBX sintered new sand), and potassium tungstate (manufactured by Nippon Inorganic Chemical Industry Co., Ltd., D50 = 1.0 μm), which is an acid hardener, was prepared. The sand was not heated. An aqueous solution in which 1.0 part by mass of potassium tungstate and 3.3 parts by mass of water as a solvent were mixed was added to 100 parts by mass of the artificial sand at a sand temperature of 25°C, and the mixture was stirred and mixed for 60 seconds to obtain wet-state molding sand.

[0209] Test Example 1 (1) Flexural strength (test piece strength (TP strength)) 200 g of various samples were weighed into a metal container. The binders for coating described in Tables 4 to 6 were added to all the molding sand samples. Four types of binders for coating with different furfuryl alcohol contents were prepared. Their compositions are shown in Table 3. The mixture was prepared by stirring for 5 seconds using a stirrer. The obtained mixture was packed into a mold of 10 mm × 10 mm × 60 mm and left for 30 minutes under the conditions of a temperature of 23 to 25°C and a humidity of 40 to 45%, and then demolded. In this way, test pieces for measuring the flexural strength were produced.

[0210] In addition, based on the prior investigations by the present inventors, it has been previously confirmed that in the strength reproduction test in a laboratory without using a 3D printer, the stirring time should be set to 5 seconds in order to reproduce the strength after 3D lamination. In order to represent the condition where the molding sand and the binder for coating cannot be forcibly mixed, which is called 3D lamination, in the laboratory, it is important to make the stirring time extremely short.

[0211] Thereafter, using the test pieces, the three-point bending strength was measured using an IMADA force gauge "ZTS-1000N" at (a) immediately after demolding (30 minutes later), (b) 3 hours later, and (c) 24 hours later, respectively. The results are shown in Tables 4 to 6. The strength after 3 hours is 25 kg / cm 2 Those that met the above criteria were considered qualified.

[0212]

Table 3

[0213] (2) Measurement of humidity in sand grain gaps The humidity measurement of the molding sand was carried out using a digital thermometer and hygrometer "605-H1" manufactured by Testo in a room adjusted to a temperature of 23 to 25°C and a humidity of 40 to 45%. Approximately 300 g of the molding sand sample was collected in a glass beaker, and after inserting the sensor part of the digital thermometer and hygrometer completely into the sample, it was left standing for 5 minutes. The value (humidity) shown after 5 minutes was read. The results are shown in Tables 4 to 6.

[0214] (3) Fluidity test The fluidity test was conducted in a room adjusted to a temperature of 23 - 25°C and a humidity of 40 - 45%. Various casting sands were prepared. After weighing 100 g of casting sand into a paper cup, it was gently tamped down. This operation was repeated until the weight of the casting sand in the paper cup reached 300 g. Then, a metal bat was placed over the paper cup containing the casting sand, and the paper cup and the bat were flipped together so that their positions would not shift, and they were placed on a horizontal surface. The paper cup was gently pulled out, and the shape of the sand pile after it was completely pulled out was visually inspected. Those sand piles that collapsed were marked as "○", and those that maintained the shape of the sand pile were marked as "×". The results are shown in Tables 4 - 6.

[0215]

Table 4

[0216]

Table 5

[0217]

Table 6

[0218] As is clear from the results in Tables 4 - 6 and Figure 6, it can be seen that the casting sand of the examples can exhibit the desired strength and fluidity. It can be understood that the presence of the organic layer dissolved in furfuryl alcohol enables the acid curing agent to be uniformly supported on the sand grain surface. It was also confirmed that a high strength of about 40 kg / cm 2 can be obtained on average 3 hours after molding without selecting the sand type, the grain size of the sand grains, the type of coating agent or the acid curing agent.

[0219] In contrast, in Comparative Examples 1 and 2, the target flexural strength was not obtained. It is presumed that the acid curing agent could not be uniformly dispersed due to the absence of the organic layer. Regarding Comparative Example 2, even though the addition amount of the curing agent or the coating binder was increased compared to Comparative Example 1, no improvement in flexural strength was observed. From this, it can be seen that the organic layer of the present invention plays a role in improving the mold strength.

[0220] In Comparative Example 3, an excessive amount of palmitic acid, which is a coating agent, was added, inhibiting the curing reaction, and the reaction with the coating binder did not proceed much, so it is presumed that the strength did not increase.

[0221] In Comparative Example 4, since the acid curing agent could not be uniformly supported on the sand grain surface due to insufficient addition amount of palmitic acid, which is a coating agent, it is considered that the desired flexural strength could not be obtained.

[0222] In Comparative Example 5, an excessive amount of acid curing agent was added, resulting in a large amount of reaction water being generated at once during the curing of the coating binder, stopping the polymerization of the furan resin precursor and causing internal curing defects.

[0223] In Comparative Example 6, since the addition amount of the acid curing agent was insufficient, the curing reaction did not proceed sufficiently, and it is considered that the target flexural strength was not obtained.

[0224] In Comparative Example 7, an excessive amount of the furan resin composition "Constitution 1", which is a coating agent, was added, resulting in a large amount of reaction water being generated at once during the curing of furan, and there was not enough heat of reaction for curing, so it is considered that the target flexural strength was not obtained.

[0225] In Comparative Example 8, since the addition amount of the furan resin composition "Constitution 1", which is a coating agent, was insufficient, Constitution 1 and the acid curing agent were completely cured on the sand grain surface. Therefore, it could not play the auxiliary role of strength expression, which is the original role of the coating agent, resulting in insufficient strength.

[0226] In Comparative Example 9, since the amount of water contained in the aqueous solution of the acid curing agent was excessive, the heat of reaction generated during furan curing was suppressed, and the polymerization of the furan resin precursor stopped. As a result, it is considered that internal curing failure occurred.

[0227] Test Example 2 (1) Preliminary drying of test pieces Using a VX500 (manufactured by Voxeljet), a 3D printer device, in an environment with a temperature of 23 - 25°C and a humidity of 40 - 45%, a test piece of 10 mm × 10 mm × 200 mm was formed from the casting sand sample prepared under the conditions of Example 11 described in Table 5.

[0228] The thickness of the casting sand discharged from the recoater was set to 300 μm to form a layer of the casting sand sample. The coating binder of Preparation Example 1 described in Table 3 was sprayed from the printer head within a predetermined region on the laminated casting sand sample. These steps were repeated until the test piece reached a predetermined thickness.

[0229] After 30 minutes had elapsed since the completion of the shaping, the test piece in the shaping box was taken out, and after removing the uncured casting sand adhering to the test piece with a brush and then a blower, preliminary drying was performed in a firing furnace set at 50°C (Example 22), 100°C (Example 23), and 180°C (Example 24), respectively.

[0230] Also, a casting sand sample prepared under the conditions of "Preparation Example 5" described in Table 7 was prepared. The method for preparing the casting sand sample is shown below. 5 kg of new sand of mullite - based sintered artificial sand (Cerabeads #1450, manufactured by Itochu Ceramtec Co., Ltd., angle of repose 31°) (CBX sintered new sand) with AFS108, the furan resin composition "Constitution 1" in Table 1, and the curing agent "Constitution 3" in Table 8 were prepared. Table 9 shows the solubility (measured value) of the heteropolyacid in water used in the examples and the solubility (measured value) of the curing agent in Table 8 in water.

[0231] With the sand temperature of the artificial sand reaching 35°C, 0.3 parts by mass of the furan resin composition of Configuration 1 was added to 100 parts by mass of the artificial sand and stirred and mixed in a kneader for 30 seconds. The sand temperature was 41°C. Next, 0.3 parts by mass of the curing agent of "Configuration 3" and 0.3 parts by mass of water as a solvent were added to the obtained mixture with respect to 100 parts by mass of the artificial sand and mixed in a kneader for 30 seconds. Finally, as a drying process, stirring was continued for 240 seconds while blowing cold air (air) into the kneader until the sand temperature reached 60°C, and then it was discharged from the kneader to obtain foundry sand.

[0232] The coating binder of Preparation Example 3 described in Table 3 was prepared in the printer head, and test pieces were produced in the same environment and method as above. The test pieces were pre-dried in a firing furnace set at 100°C (Comparative Example 11). Also, those without pre-drying (Comparative Example 10) were produced.

[0233]

Table 7

[0234]

Table 8

[0235]

Table 9

[0236] (2) Drying of the aqueous coating agent The pre-dried test pieces were dipped in the slurry of "Preparation Example 6" described in Table 10, which is an aqueous coating agent. After pulling the test pieces out of the slurry, the coating film of Preparation Example 6 was immediately dried in a firing furnace at 100°C for 60 minutes. The test pieces before pre-drying and after the drying of the coating film of Preparation Example 6 after pre-drying were overlapped and arranged, and as a result of visual observation, for those with a gap observed between the test pieces, the width (mm) of the gap was measured as those with deformation, and those without a gap observed were regarded as "none" as those without deformation. The results are shown in Table 11.

[0237]

Table 10

[0238]

Table 11

[0239] As is also clear from the results of Examples 22 to 24 described in Table 11, the test pieces of the examples did not show any deformation even after the water-based coating agent was dried.

[0240] On the other hand, in Comparative Examples 10 to 11, since heteropolyacid was not used as the curing agent, the deformation of the test pieces became remarkable without pre-drying (Comparative Example 10), and it can be seen that the deformation of the test pieces cannot be avoided even if pre-dried.

[0241] As described above, in the case of molding sand having an organic layer, by introducing heteropolyacid as an acid curing agent, even if a water-based coating agent is applied to the mold formed by the molding sand, it is possible to effectively suppress or prevent the deformation thereof.

Claims

1. Casting sand used for three-dimensional laminated modeling, (1) The particles constituting the casting sand include (a) sand grains and (b) an organic layer formed on the surface of the sand grains, (2) The organic layer contains a furan resin precursor or a fatty acid having a melting point of 40 to 75°C and a heteropolyacid, Casting sand for three-dimensional laminated modeling, characterized in that.

2. The casting sand for three-dimensional laminated modeling according to claim 1, wherein the heteropolyacid contains at least one of silicotungstic acid and phosphotungstic acid.

3. The casting sand for three-dimensional laminated modeling according to claim 1, wherein 0.5 to 2.5 parts by mass of heteropolyacid is contained per 100 parts by mass of sand grains.

4. The casting sand for three-dimensional laminated modeling according to claim 1, wherein solid particles of heteropolyacid are supported on a carrier containing a furan resin precursor or a fatty acid having a melting point of 40 to 75°C in the organic layer.

5. The casting sand for three-dimensional laminated modeling according to claim 1, wherein the organic layer has an aqueous wetting layer containing heteropolyacid formed on the surface of the sand grains and a hydrophobic layer containing a furan resin precursor or a fatty acid having a melting point of 40 to 75°C, and the surface of the aqueous wetting layer is covered by the hydrophobic layer.

6. A three-dimensional laminated modeling kit including the casting sand for three-dimensional laminated modeling according to any one of claims 1 to 5 and a coating binder.

7. A method for manufacturing casting sand for three-dimensional laminated modeling, (1) By mixing at least sand grains and a coating agent containing a furan resin precursor or a fatty acid having a melting point of 40 to 75°C at 100°C or lower, a step of obtaining precursor particles coated with a coating layer containing the furan resin precursor or fatty acid on the surface of the sand grains, and (2) By mixing the precursor particles and solid particles of heteropolyacid at 100°C or lower, a step of obtaining composite particles in which the solid particles are supported on the coating layer on the surface of the precursor particles, A method for manufacturing casting sand, characterized by including.

8. A method for manufacturing casting sand for three-dimensional laminated modeling, (1) By mixing at least sand grains and an aqueous solution of heteropolyacid at 100°C or lower, a step of obtaining precursor particles coated with an aqueous wetting layer containing the aqueous solution on the surface of the sand grains, (2) By mixing the precursor particles and a coating agent containing a furan resin precursor or a fatty acid having a melting point of 40 to 75°C at 100°C or lower, a step of obtaining composite particles in which the aqueous wetting layer is covered with a hydrophobic layer containing the fatty acid, A method for manufacturing casting sand, characterized by including.

9. The manufacturing method according to claim 7 or 8, further comprising a step of adding 0.5 parts by mass or less of a silane coupling agent with respect to 100 parts by mass of the abrasive grains 100.

10. A method for manufacturing a sand mold using the casting sand for three-dimensional laminated molding according to any one of claims 1 to 5, (1) a step of obtaining a molded body by repeating in sequence a step of forming a layer containing the casting sand and a step of solidifying a predetermined region of the layer by adding a binder for coating to the predetermined region of the layer, and (2) a step of obtaining a sand mold by heat-treating the molded body not containing an aqueous mold coating agent at 40 to 250°C in the atmosphere or in an inert gas atmosphere The method for manufacturing a sand mold, characterized by including the above steps.

11. A sand mold for casting an iron-based material, comprising the casting sand for three-dimensional laminated molding according to any one of claims 1 to 5.

12. The sand mold for casting an iron-based material according to claim 11, further comprising an aqueous mold coating agent.

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