Method for manufacturing 3D additively manufactured objects, and kit for 3D additive manufacturing

Abstract

To provide: a manufacturing method for a three-dimensional additive manufactured article that enables manufacturing, in a good working environment, a three-dimensional additive manufactured article with practical strength; and a three-dimensional additive manufacturing kit.SOLUTION: The manufacturing method for a three-dimensional additive manufactured article includes: a step (a) of spreading, in layers, a coated material obtained by coating a fire-resistant granular material with polycarboxylic acid; and a step (b) of ejecting a sugar binder onto a desired region of the coated material spread in layers. The method repeats the step (a) and the step (b) until a target three-dimensional additive manufactured article is formed. The three-dimensional additive manufacturing kit includes: a coated material obtained by coating a fire-resistant granular material with polycarboxylic acid; and a sugar binder, each of which is independent of the other.SELECTED DRAWING: None

Description

Technical Field

[0005] ,

[0001] The present invention relates to a method for manufacturing a three-dimensional laminated object and a kit for three-dimensional lamination molding.

Background Art

[0002] Conventionally, a self-hardening mold is known as one of the molds for casting (hereinafter, also simply referred to as "mold"). A self-hardening mold is obtained by adding and kneading a binder (acid-curable binder) mainly composed of a furan resin or the like and an acid catalyst (hardener) such as sulfuric acid or xylene sulfonic acid to a refractory granular material such as silica sand, and then filling the obtained kneaded sand into a wooden mold or a resin mold (hereinafter, these are collectively referred to as "pattern"), and curing the binder.

[0003] A liquid obtained by melting a metal such as iron, copper, or aluminum at a high temperature is poured into the mold to obtain a casting, but the acid-curable binder may be thermally decomposed during pouring to generate gas (pyrolysis gas). In addition, when a large amount of acid catalyst is used for the purpose of accelerating the curing rate, sulfur oxides such as sulfurous acid gas are likely to be generated during pouring. Thus, when gas is generated during pouring, the working environment deteriorates.

[0004] Therefore, a method for manufacturing a mold using a sugar binder instead of an acid-curable binder as a binder has been proposed. For example, Patent Documents 1 and 2 disclose a method for manufacturing a mold by filling a binder-coated refractory material in which a solid coating layer containing a saccharide as a binder is coated on the surface of a refractory aggregate into a pattern and heating to melt the saccharide, and then solidifying or curing the saccharide. Since saccharides are carbohydrates, even if they are thermally decomposed, only carbon dioxide gas, water, etc. are generated, and the working environment is unlikely to deteriorate. In addition, since the adhesiveness is exhibited by solidifying or curing the melted saccharide, there is no need to use an acid catalyst.

Prior Art Documents

Patent Documents

[0006] By the way, manufacturing molds with complex shapes inevitably requires increasing the number of models, which complicates the process. Furthermore, even if the number of models can be increased, if the mold cannot be removed from the models, the mold cannot be manufactured. To address these issues, a method of manufacturing molds using 3D additive manufacturing has recently been proposed, which allows for the direct production of molds without the need for physical models.

[0007] When manufacturing a mold by three-dimensional additive manufacturing using binder-coated refractories described in Patent Documents 1 and 2, in order to obtain a mold of the desired shape, it is necessary to repeat the steps of layering the binder-coated refractories and injecting water into a desired area of ​​the layered binder-coated refractories to gelatinize the sugars, until the desired three-dimensional additive manufactured object is formed, and then perform a heat treatment. However, if the gelatinized sugars simply dry and solidify, the refractory aggregates are not sufficiently bonded together, resulting in insufficient strength. Therefore, it is difficult to remove the desired 3D additively manufactured object from the areas where water has not been injected during the heat treatment. Consequently, the entire object is heat-treated without removing the desired 3D additively manufactured object, causing the sugars in the areas where water has not been injected to melt and then harden, resulting in an unsuccessful 3D additively manufactured object of the desired shape. Thus, refractories coated with binders, in which refractory aggregates are coated with sugars, are unsuitable for the manufacture of molds using 3D additive manufacturing.

[0008] The present invention aims to provide a method for manufacturing 3D additively manufactured objects that can be produced in a good working environment and with practical strength, as well as a 3D additive manufacturing kit. [Means for solving the problem]

[0009] The present invention has the following aspects. [1] The process includes (a) laying out layers of a coating material in which polycarboxylic acids are coated on a refractory granular material, and (b) injecting a sugar binder into a desired area of ​​the layered coating material. A method for manufacturing a three-dimensional additively manufactured object, comprising repeating the above steps (a) and (b) until the desired three-dimensional additively manufactured object is produced. [2] A method for manufacturing a three-dimensional additively fabricated object according to [1], further comprising a step (c) of curing the sugar binder by heating, at least after the last step (b). [3] A kit for 3D additive manufacturing comprising a coating material in which polycarboxylic acids are coated onto a refractory granular material, and a sugar binder, each being independent of the other. [Effects of the Invention]

[0010] According to the present invention, a method for manufacturing a 3D additively manufactured object and a 3D additive manufacturing kit can be provided, which enable the production of 3D additively manufactured objects with a good working environment and practical strength. [Brief explanation of the drawing]

[0011] [Figure 1] This graph shows the calibration curve created in Example 1-1. [Figure 2] This graph shows the calibration curve created in Example 1-2. [Figure 3] This graph shows the calibration curve created in Example 1-3. [Figure 4] This graph shows the calibration curve created in Example 1-4. [Modes for carrying out the invention]

[0012] [Method for manufacturing three-dimensional laminated object] Hereinafter, an embodiment of the method for manufacturing a three-dimensional laminated object of the present invention will be described. The method for manufacturing a three-dimensional laminated object of this embodiment includes the following steps (a) and (b), and the three-dimensional laminated object is manufactured by repeating steps (a) and (b) until the target three-dimensional laminated object is formed. The method for manufacturing a three-dimensional laminated object of this embodiment preferably further includes the following step (c) at least after the last step (b).

[0013] [Coating material][[ID=eleven]] [[ID=twelve]]The coating material used in the present invention is obtained by coating refractory granular materials with polycarboxylic acids. [[ID=thirteen]] [[ID=fourteen]]Examples of the refractory granular materials include sand, ceramic powder, metal powder, and the like. [[ID=fifteen]] [[ID=sixteen]]These refractory granular materials may be used alone or in combination of two or more. [[ID=seventeen]]<unk>0000087< / unk>[[ID=eighteen]]

[0014] [[ID=nineteen]] [[ID=twenty]]Examples of the sand include natural sand such as silica sand, chromite sand, zircon sand, olivine sand, amorphous silica, alumina sand, and mullite sand; artificial sand, and the like. In addition, used artificial sand or natural sand recovered (recovered sand), or those obtained by recycling these (recycled sand) can also be used. These sands may be used alone or in combination of two or more. [[ID=twenty-one]] [[ID=twenty-two]]Artificial sand is generally obtained from bauxite as a raw material by any of the melting method (atomization method), sintering method, and flame melting method. Specific conditions such as those of the melting method, sintering method, and flame melting method are not particularly limited. For example, artificial sand may be manufactured using known conditions described in JP-A-5-169184, JP-A-2003-251434, JP-A-2004-202577, and the like. [[ID=twenty-three]] [[ID=twenty-four]]Examples of the metal include nickel, cobalt, molybdenum, iron, stainless steel, aluminum, titanium, copper, and the like. These metals may be used alone or in combination of two or more. [[ID=twenty-five]] [[ID=twenty-six]]

[0015] [[ID=twenty-seven]] The average particle diameter of the refractory granular material is preferably 10 to 300 μm, more preferably 50 to 150 μm. If the average particle diameter of the refractory granular material is at least the above lower limit value, a three-dimensional laminated molded object with high strength can be obtained. If the average particle diameter of the refractory granular material is at most the above upper limit value, a three-dimensional laminated molded object with excellent surface flatness can be obtained. The average particle diameter of the refractory granular material is the particle diameter (median diameter) corresponding to a cumulative frequency of 50% based on the volume distribution of the refractory granular material measured by the dynamic light scattering method. Also, "surface roughness" refers to the surface roughness of the three-dimensional laminated molded object in the lamination direction.

[0016] The refractory granular material is selected according to the intended use of the obtained three-dimensional laminated molded object. For example, when the three-dimensional laminated molded object is used as a mold, sand is suitable as the refractory granular material. Since natural sand is less expensive than artificial sand, from the viewpoint of suppressing production costs, it is preferable to use natural sand alone or mixed with artificial sand. Considering the refractoriness of the mold, it is preferable to use a mixture of natural sand and artificial sand. In this specification, when the refractory granular material is sand, the coating material is also referred to as "coated sand". Note that a mold is a mold for casting a casting and is disassembled to remove the casting after casting. That is, assuming that the casting is the final object (final product), the mold is ultimately assumed to be broken. On the other hand, when the three-dimensional laminated molded object is the final object (not assumed to be ultimately broken), a metal is suitable as the refractory granular material. In this specification, a three-dimensional laminated molded object obtained using a metal is also referred to as a "metal molded body".

[0017] Polycarboxylic acids serve as an acid catalyst (hardening agent). In addition, since they react with the sugar binder described later to exhibit adhesiveness, they also serve as a binder. In the present invention, the term "polycarboxylic acids" includes polycarboxylic acid salts, polycarboxylic acid anhydrides, polycarboxylic acid halides, polycarboxylic acid derivatives, etc. in addition to polycarboxylic acids.

[0018] Examples of polycarboxylic acids include citric acid, malic acid, oxalic acid, maleic acid, succinic acid, fumaric acid, tartaric acid, isophthalic acid, itaconic acid, butanetetradicarboxylic acid, myristic acid, palmitic acid, malonic acid, glutaric acid, phthalic acid, terephthalic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 5-hydroxyisophthalic acid, 3,6-dihydroxyphthalic acid, 4-hydroxyphthalic acid, methyl vinyl ether-maleic anhydride copolymer, and other polycarboxylic acids; salts of these polycarboxylic acids (polycarboxylic acid salts); anhydrides of these polycarboxylic acids (polycarboxylic acid anhydrides); halides of these polycarboxylic acids (polycarboxylic acid halides); and derivatives of these polycarboxylic acids (polycarboxylic acid derivatives). Examples of salts of polycarboxylic acids include salts of polycarboxylic acids with alkali metals (potassium, sodium, etc.), salts of polycarboxylic acids with alkaline earth metals (magnesium, calcium, etc.), salts of polycarboxylic acids with ammonium, and salts of polycarboxylic acids with alkanolamines (monoethanolamine, diethanolamine, triethanolamine, etc.). Examples of polycarboxylic acid anhydrides include those obtained by intramolecular or intermolecular dehydration condensation of polycarboxylic acids, which contain a carboxylic acid anhydride group (-CO-O-CO-). Examples of halides of polycarboxylic acids include acid chlorides and acid bromides of polycarboxylic acids. Examples of polycarboxylic acid derivatives include ester compounds of polycarboxylic acids with lower alcohols having 1 to 5 carbon atoms (methanol, ethanol, propanol, butanol, pentanol, etc.) and ester compounds of polycarboxylic acids with low molecular weight glycols (ethylene glycol, etc.). Among these, polycarboxylic acids are preferred because they are plant-derived and readily available, with citric acid and malic acid being more preferred. These polycarboxylic acids may be used individually or in combination of two or more.

[0019] The content of polycarboxylic acids is preferably 0.1 to 5 parts by mass, more preferably 0.3 to 3 parts by mass, and even more preferably 0.5 to 2 parts by mass, per 100 parts by mass of refractory granular material. If the content of polycarboxylic acids is above the lower limit, it becomes easier to obtain three-dimensional additively manufactured products with practical strength. If the content of polycarboxylic acids is below the upper limit, gas generation during pouring can be further reduced.

[0020] The refractory granular material may be coated with other components in addition to polycarboxylic acids, as needed, as long as it does not impair the effects of the present invention. Other components include monovalent carboxylic acids such as benzoic acid, o-hydroxybenzoic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid (gallic acid), 2,4,6-trihydroxybenzoic acid, salicylic acid, and anthranilic acid; sulfonic acids such as p-toluenesulfonic acid, xylenesulfonic acid, benzenesulfonic acid, and methanesulfonic acid; sulfuric acid; and phosphoric acid. These other components may be used individually or in combination of two or more. However, sulfur-containing acids such as sulfonic acid and sulfuric acid tend to generate sulfur oxides such as sulfur dioxide when poured. Therefore, the content of sulfur-containing acids such as sulfonic acid and sulfuric acid is preferably less than 0.5 parts by mass, more preferably 0.3 parts by mass or less, and even more preferably 0.1 parts by mass or less, per 100 parts by mass of refractory granular material, and it is particularly preferable that the refractory granular material is not coated with a sulfur-containing acid.

[0021] Other components, in addition to those mentioned above, include, for example, inorganic particles, zeolites, and anti-blocking agents such as lubricants. Examples of inorganic particles include silica, titania, alumina, zeolite, kaolin, talc, mica, and other silicate minerals; and diatomaceous earth. Silica may be amorphous or crystalline. It may also be natural or synthetic silica. Examples of synthetic silica include wet silica such as precipitated silica and silica gel; and dry silica such as fumed silica (flame hydrolysis silica), arc silica, plasma silica, and quartz glass (flame fused silica). Zeolites are a general term for crystalline aluminosilicates. Examples of zeolite skeletal structures include A-type, X-type, LSX-type, beta-type, ZSM-5-type, ferrielite-type, mordenite-type, L-type, and Y-type. Examples of lubricants include aliphatic hydrocarbon lubricants such as paraffin wax and carnauba wax; aliphatic amide lubricants such as higher aliphatic alcohols, ethylenebisstearate amide, and stearate amide; metal soap lubricants such as calcium stearate, barium stearate, zinc stearate, aluminum stearate, and magnesium stearate; fatty acid ester lubricants; and compound lubricants. These blocking inhibitors may be used individually or in combination of two or more.

[0022] The coating material can be obtained, for example, by adding a solution (hereinafter also referred to as "solution (α)") containing polycarboxylic acids and, if necessary, other components to a heated refractory granular material. The solvent used in solution (α) includes water, alcohol, and mixtures thereof. Examples of alcohols include methanol, ethanol, 1-propanol, and 2-propanol. The content of polycarboxylic acids relative to the total mass of solution (α) is preferably 10 to 70% by mass, and more preferably 30 to 60% by mass.

[0023] The heating temperature of the refractory granular material is preferably 250°C or lower, more preferably 200°C or lower, and even more preferably 150°C or lower. If the temperature of the refractory granular material is below the above upper limit, the thermal decomposition of polycarboxylic acids can be suppressed. In particular, when obtaining a dry coating material, the heating temperature of the refractory granular material is preferably above the boiling point of the solvent contained in solution (α), more preferably 100 to 250°C, even more preferably 100 to 200°C, and particularly preferably 100 to 150°C. However, if the solvent contained in solution (α) is an alcohol, it has a lower boiling point than water and evaporates easily even below the boiling point of alcohol. Therefore, the heating temperature of the refractory granular material is not limited to the above range, and when the solvent contained in solution (α) is an alcohol, a dry coating material may be obtained even if the heating temperature of the refractory granular material is above 60°C and below 100°C. On the other hand, when obtaining a wet coating material, the heating temperature of the refractory granular material is preferably below the boiling point of the solvent contained in solution (α), more preferably 60°C or less, even more preferably 10 to 50°C, and particularly preferably 20 to 30°C. The coating material may be in a dry state or in a wet state as long as it can be layered in 3D additive manufacturing, but it is preferable that it be in a dry state.

[0024] <Sugar Binder> The sugar binder used in this invention serves as a binder. Examples of sugar binders include carbohydrates such as monosaccharides, oligosaccharides, and polysaccharides; and sugar alcohols. In this specification, "oligosaccharide" refers to a compound of 2 to 10 monosaccharides, and "polysaccharide" refers to a compound of 11 or more monosaccharides.

[0025] Examples of monosaccharides include glucose, fructose, mannose, galactose, ribose, and xylose. Examples of oligosaccharides include disaccharides such as sucrose, maltose, lactose, trehalose, isomaltose, and cellobiose; trisaccharides such as maltotriose and raffinose; maltooligosaccharides; isomaltoligosaccharides; fructooligosaccharides; mannooligosaccharides; and galactooligosaccharides. Examples of polysaccharides include starch, dextrin, zanthangum, curdlan, pullulan, cycloamylose, chitin, cellulose, and polydextrose. Examples of starches include unprocessed starch and processed starch. Specifically, these include unprocessed starches such as potato starch, corn starch, high amylose, sweet potato starch, tapioca starch, sago starch, rice starch, and amaranth starch, as well as processed starches such as roasted dextrin, enzyme-modified dextrin, acid-treated starch, oxidized starch, dialdehyde-treated starch, ether-treated starch (carboxymethyl starch, hydroxyalkyl starch, cationic starch, methylol-treated starch, etc.), esterified starch (acetic acid starch, phosphate starch, succinate starch, octenyl succinate starch, maleate starch, higher fatty acid esterified starch, etc.), cross-linked starch, kraft starch, and moist heat-treated starch. Examples of sugar alcohols include maltitol, sorbitol, ribitol, mannitol, arabitol, galactitol, lactitol, xylitol, sucrose, erythritol, and inositol. Sugar, whose main component is sucrose (table sugar), can be classified into various types such as refined white sugar, granulated sugar, white granulated sugar, light brown sugar, and brown sugar, depending on the raw materials and manufacturing methods. All of these can be used as sugar binders in this invention. These sugar binders may be used individually or in combination of two or more.

[0026] <Process (a), process (b)> Step (a) is the process of laying out the covering material in layers. Step (b) is the step of injecting a sugar binder into a desired area of ​​a layered coating material. In the manufacturing method for a 3D additively manufactured object according to this embodiment, steps (a) and (b) are repeated until the desired 3D additively manufactured object is produced.

[0027] Processes (a) and (b) are carried out, for example, using a 3D additive manufacturing apparatus employing a printing method, as follows. A three-dimensional additive manufacturing apparatus is preferably equipped with a blade mechanism, a printing nozzle head mechanism, and a build table mechanism. Furthermore, it is preferable to have a control unit that controls the operation of each mechanism using three-dimensional data of the object to be built. The blade mechanism includes a recoater and laminates a coating material to a predetermined thickness onto the surface of the metal case or onto the upper layer of the molded part that has been bonded with a sugar binder. The printing nozzle head mechanism creates the structure layer by layer by printing with a sugar binder onto the stacked coating material and bonding the coating material together. The build table mechanism lowers by the distance of one layer after each layer has been built, enabling additive manufacturing at a predetermined thickness.

[0028] First, using a 3D additive manufacturing apparatus employing a printing method, a coating material is deposited onto the bottom surface of a metal case installed in the 3D additive manufacturing apparatus by a blade mechanism with a recoater (step (a)). Next, a printing nozzle head mechanism is used to scan a desired area of ​​the deposited coating material based on data obtained from 3D CAD design of the desired 3D additive manufacturing object, and the sugar binder is printed (injected) (step (b)). The bottom surface of the metal case serves as a build table and can move up and down. After printing the sugar binder, the bottom surface of the metal case (build table) is lowered by one layer, and the coating material is deposited in the same manner as before (step (a)), and the sugar binder is printed on top of it (step (b)). These deposition and printing operations are repeated until the desired 3D additive manufacturing object is produced. The thickness of one layer is preferably 100 to 500 μm, and more preferably 100 to 300 μm. Furthermore, when manufacturing a metal molded body using a coating material in which the refractory granular material is metal, it is preferable to use a metal 3D printer.

[0029] It is preferable to pre-dissolve or dilute the sugar binder in a solvent to a concentration that is easily ejected from the printing nozzle head mechanism, and to use it in solution form. That is, it is preferable to eject a solution containing the sugar binder (hereinafter also referred to as "solution (β)") in step (b). The solvent used in solution (β) includes water, alcohol, and mixtures thereof. Examples of alcohols include methanol, ethanol, 1-propanol, and 2-propanol.

[0030] When printing the sugar binder, the amount applied should preferably be such that the mass ratio of the sugar binder to the polycarboxylic acids in one layer of the coating material in the printed area is 90:10 to 10:90, more preferably 80:20 to 20:80, even more preferably 70:30 to 30:70, particularly preferably 60:40 to 40:60, and most preferably 50:50. By applying the sugar binder so that the mass ratio of the sugar binder to the polycarboxylic acids is within the above range, sufficient curing is possible through the reaction between the sugar binder and the polycarboxylic acids. In particular, if the mass ratio of the sugar binder to the polycarboxylic acids is within the range of 50:50 to 20:80, it tends to be easier to obtain 3D additive manufactured objects with excellent water resistance. Therefore, when the 3D additive manufactured object is a mold, the strength of the mold can be well maintained even when casting in a high-humidity environment.

[0031] Furthermore, the amount of sugar binder applied when printing is preferably 0.5 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, and even more preferably 0.5 to 2 parts by mass, when the mass of the refractory granular material in one layer of the coating material in the printed area is 100 parts by mass. Sufficient bonding properties can be obtained if the ratio of sugar binder to the refractory granular material is above the above lower limit. The bonding effect tends to be obtained more easily as the ratio of sugar binder increases, but if it increases too much, the effect will only plateau. Therefore, the ratio of sugar binder is preferably 10 parts by mass or less.

[0032] In step (a), the coating material may be used in a state mixed with the blocking inhibitor. That is, a mixture (M) containing the coating material and the blocking inhibitor may be laid in layers. The mixture (M) is obtained, for example, by adding solution (α) to heated refractory granular material to produce a coating material, and then mixing the resulting coating material with an anti-blocking agent. Solution (α) may or may not contain an anti-blocking agent as another component. If the mixture (M) is laid in layers in step (a), then in step (b), a sugar binder is injected into a desired area of ​​the layered mixture (M).

[0033] The resulting 3D additively manufactured object is formed while embedded in the coating material powder. As the injected sugar binder dries and solidifies, the refractory granular materials bond to a certain extent, allowing the 3D additively manufactured object to be removed from the coating material powder. If any coating material from areas where the sugar binder is not printed (non-printed areas) is attached to the surface of the removed 3D additively manufactured object, it should be removed using a brush or vacuum cleaner.

[0034] After removing the 3D additively manufactured object from the coating material powder, it is preferable to perform the following step (c) in order to increase the strength of the 3D additively manufactured object. Furthermore, if the coating material adhering to the periphery of the extracted 3D additively manufactured object is difficult to remove, it is preferable to perform the following step (c). Alternatively, the following step (c) may be performed with the 3D additively manufactured object embedded in the coating material powder, without removing the 3D additively manufactured object from the coating material powder.

[0035] <Process (c)> Step (c) is a step in which the sugar binder is hardened by heating, at least after the last step (b). The number of times step (c) is performed may be once or two or more times. If step (c) is performed only once, then step (c) is performed only after the last step (b). If step (c) is performed two or more times, step (c) is performed at least once after each step (b), except for the last step (b). For example, steps (a), (b), and (c) are repeated in this order until the desired 3D additively manufactured object is created. If the 3D additive manufactured object can be removed from the coating material powder after the final step (b), only the removed 3D additive manufactured object may be heated. In this case, the 3D additive manufactured object may be heated with the non-printed coating material adhering to its surroundings. Alternatively, the 3D additive manufactured object may be heated while embedded in the coating material powder.

[0036] The heating temperature in step (c) is preferably 100 to 300°C, more preferably 130 to 290°C, even more preferably 150 to 280°C, even more preferably 160 to 270°C, particularly preferably 170 to 260°C, and most preferably 180 to 250°C. If the heating temperature is above the lower limit, the sugar binder hardens easily. In particular, if the heating temperature is 150°C or higher, a 3D additively manufactured product with practical strength is easily obtained. Furthermore, if the heating temperature exceeds 150°C, a 3D additively manufactured product with excellent water resistance is easily obtained. Therefore, if the 3D additively manufactured product is a mold, the strength of the mold can be well maintained even when casting in a high-humidity environment. If the heating temperature is below the upper limit, the thermal decomposition of polycarboxylic acids and sugar binder can be suppressed. The heat treatment may be performed using a dryer, or, if the 3D stacking apparatus is equipped with a heat treatment mechanism, the heat treatment may be performed inside the metal case of the 3D stacking apparatus.

[0037] Heating causes the sugar binder to melt, and then solidify or harden, resulting in strong bonding between the refractory granular materials. Furthermore, when the sugar binder melts, reactions with polycarboxylic acids (such as esterification) proceed, making polymerization easier. This increases the hardening properties compared to when the sugar binder solidifies or hardens alone, resulting in stronger bonding between the refractory granular materials. From the viewpoint of ensuring that the reaction between the sugar binder and polycarboxylic acids proceeds sufficiently, it is preferable to carry out step (c).

[0038] When step (c) is performed with the 3D additively manufactured object embedded in the coating material powder, after step (b) and then step (c), the coating material in areas where the sugar binder is not printed (non-printed areas) is removed with a brush or vacuum cleaner to extract the 3D additively manufactured object. Heating polymerizes the sugar binder and polycarboxylic acids, causing the refractory granular materials to bond more strongly, thus increasing the strength of the 3D additively manufactured object and allowing it to maintain its shape well. Therefore, the 3D additively manufactured object can be easily extracted from the coating material powder. Since no reaction occurs between the sugar binder and polycarboxylic acids in the non-printed areas, the refractory granular materials do not bond to each other, and the coating material in the non-printed areas can be easily removed.

[0039] Furthermore, when manufacturing a metal molded body, after the final step (b), step (c) may be performed, followed by a degreasing step and a sintering step as needed.

[0040] <Effects and Effects> According to the method for manufacturing three-dimensional additive-built objects of the present invention described above, since a sugar binder is used as a binder, when the three-dimensional additive-built object obtained by the present invention is used as a mold, even if thermal decomposition occurs during pouring, only carbon dioxide and water are generated, and the working environment during pouring is not likely to deteriorate. Furthermore, since the present invention uses a coating material in which polycarboxylic acids are coated onto a refractory granular material, there is no need to use sulfur-containing acids such as sulfonic acid or sulfuric acid as an acid catalyst. Therefore, when the three-dimensional additive manufactured product obtained by the present invention is used as a mold, the working environment during pouring is less likely to deteriorate, from the viewpoint that sulfur oxides such as sulfur dioxide are less likely to be generated during pouring.

[0041] When manufacturing metal molded bodies, the binder is typically cured, followed by a degreasing process and a sintering process. During these degreasing and sintering processes, the binder can decompose thermally, generating gases (thermal decomposition gases), or sulfur oxides such as sulfur dioxide can be generated due to acid catalysts such as sulfuric acid or xylene sulfonic acid, leading to a deterioration of the working environment. However, in the present invention, since a coating material in which polycarboxylic acids are coated onto a refractory granular material and a sugar binder are used, even if a degreasing process and a sintering process are performed after step (c), thermal decomposition gases and sulfur oxides are less likely to be generated, and the working environment in the manufacturing process of metal molded bodies is less likely to deteriorate.

[0042] Thus, in this invention, since a coating material in which polycarboxylic acids are coated onto a refractory granular material and a sugar binder are used, the working environment during pouring and the manufacturing process is good, and three-dimensional additively manufactured objects with practical strength can be produced. Furthermore, because three-dimensional additive manufacturing is employed, even three-dimensional additively manufactured objects with complex shapes can be easily manufactured. Furthermore, since the sugar binder is a plant-derived binder made from plants, according to the present invention, carbon-neutral 3D additively fabricated objects can be manufactured, reducing the use of fossil fuels such as petroleum and coal, and contributing to the prevention of global warming (reduction of carbon dioxide) and the creation of a circular economy through carbon neutrality.

[0043] [3D additive manufacturing kit] The 3D additive manufacturing kit of the present invention independently comprises a coating material in which polycarboxylic acids are coated on a refractory granular material, and a sugar binder. The 3D additive manufacturing kit may further independently comprise an anti-blocking agent. Here, "possessing independently" means that each component exists in a state where it is not mixed with or in contact with one another. A 3D additive manufacturing kit may be an assembly of containers, for example, comprising a first container containing coating material and a second container containing a sugar binder. The first container may further contain an anti-blocking agent as needed. That is, the coating material may be contained in the first container as a mixture with the anti-blocking agent. Furthermore, the 3D additive manufacturing kit may be an assembly of containers comprising a first container containing a coating material, a second container containing a sugar binder, and a third container containing an anti-blocking agent.

[0044] Examples of coating materials that constitute a kit for 3D additive manufacturing include the coating materials previously exemplified in the description of the method for manufacturing 3D additive manufactured objects according to the present invention. Examples of sugar binders that constitute a 3D additive manufacturing kit include the sugar binders previously exemplified in the description of the method for manufacturing 3D additive manufactured objects according to the present invention. Examples of anti-blocking agents that constitute a kit for 3D additive manufacturing include the anti-blocking agents previously exemplified in the description of the method for manufacturing 3D additive manufactured objects according to the present invention.

[0045] In the method for manufacturing a three-dimensional additive manufactured object according to the present invention described above, the three-dimensional additive manufactured object may be manufactured using the three-dimensional additive manufacturing kit of the present invention. Specifically, the process involves repeatedly laying out the coating material taken from the first container in layers, and injecting the sugar binder taken from the second container into a desired area of ​​the layered coating material, until the desired three-dimensional additively manufactured object is formed. In this process, it is preferable to perform the above-described step (c). If the first container also contains an anti-blocking agent, the coating material will be used in a state mixed with the anti-blocking agent. If the 3D additive manufacturing kit has the coating material and anti-blocking agent separately, the coating material taken from the first container and the anti-blocking agent taken from the third container may be mixed to prepare a mixture (M), and then the resulting mixture (M) may be laid in layers.

[0046] According to the 3D additive manufacturing kit of the present invention described above, since it contains a sugar binder as a binder, when the 3D additive manufactured object obtained using the 3D additive manufacturing kit of the present invention is a mold, even if thermal decomposition occurs during pouring, only carbon dioxide and water are generated, and the working environment during pouring is not likely to deteriorate. Furthermore, since the 3D additive manufacturing kit has a coating material in which polycarboxylic acids are coated onto a refractory granular material, there is no need to use sulfur-containing acids such as sulfonic acid or sulfuric acid as an acid catalyst. Therefore, when the 3D additive manufactured object obtained using the 3D additive manufacturing kit of the present invention is used as a mold, the working environment during pouring is less likely to deteriorate, from the viewpoint that sulfur oxides such as sulfur dioxide are less likely to be generated during pouring. Furthermore, when manufacturing a metal molded body using the 3D additive manufacturing kit of the present invention, even if a degreasing step and a sintering step are performed after step (c), thermal decomposition gases and sulfur oxides are less likely to be generated, and the working environment is less likely to deteriorate during the manufacturing process of the metal molded body.

[0047] Thus, by using the 3D additive manufacturing kit of the present invention, it is possible to manufacture 3D additively manufactured objects with practical strength while maintaining a good working environment during pouring and the manufacturing process. Furthermore, since the sugar binder is a plant-derived binder made from plants, the 3D additive manufacturing kit of the present invention can be used to manufacture carbon-neutral 3D additive manufactured objects, thereby reducing the use of fossil fuels such as petroleum and coal, and contributing to the prevention of global warming (reduction of carbon dioxide) and the creation of a circular economy through carbon neutrality. [Examples]

[0048] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The materials used in each example are shown below. The various measurement methods are also described below. Examples 1-1 to 1-4 below are examples, examples 1-5 and 1-6 are comparative examples, and examples 2-1 to 2-15, 3-1 to 3-3, 4-1 and 4-2 are reference examples.

[0049] [Measurement and Evaluation Methods] <Measurement of bending strength> The bending strength of the test pieces obtained in each example and comparative example was measured using the measurement method described in JACT Test Method SM-1.

[0050] <Evaluation of water resistance> A test piece, whose bending strength had been measured, was placed in a test tube containing 10g of pure water, and stirred for 10 seconds using a test tube mixer. After stirring, the test piece was allowed to stand, and the condition of the test piece and the color of the pure water were visually inspected. The water resistance was then evaluated according to the following criteria. <<Status>> ○: The test piece has not disintegrated. △: The test piece is slightly disintegrated. ×: The test piece has collapsed. <<Color>> ○: The color of the pure water does not change and it is colorless and transparent. △: The pure water is slightly colored. ×: The pure water is colored.

[0051] [Test 1] As a refractory granular material, artificial sand obtained by the melting method (Ito Kiko Co., Ltd., "Alsand #1000", average particle size 120 μm) was used. Citric acid or malic acid was used as the polycarboxylic acid. Maltitol, maltose, or Pure Toth L (manufactured by Gun-ei Chemical Industry Co., Ltd.) were used as the sugar binder. Pure Toth L contains 55% by mass or more of maltotriose relative to the total solid content. Solution (α1) was prepared by dissolving citric acid in water to a concentration of 50% by mass. Solution (α2) was prepared by dissolving malic acid in water to a concentration of 50% by mass. After dissolving maltitol in water to a concentration of 30% by mass, the solution (β1) was prepared by filtering it through a wire mesh with a mesh size of 50 μm. After dissolving maltose in water to a concentration of 30% by mass, the solution (β2) was prepared by filtering it through a wire mesh with a mesh size of 50 μm. Pure Toth L was dissolved in water to a concentration of 40% by mass, and then filtered through a wire mesh with a mesh size of 50 μm to prepare solution (β3). The viscosity and specific gravity at 25°C were measured for solutions (β1) to (β3). The results are shown in Table 1. Viscosity was measured using a Type B viscometer under the conditions of a rotor speed of 60 rpm and a measurement temperature of 25°C. A Type 1 rotor was used. Specific gravity was measured in accordance with the "Method for measuring the density and specific gravity of liquids" in JIS Z 8804:2012.

[0052] [Table 1]

[0053] <Example 1-1> (Preparation of coating material) To 100 parts by mass of refractory granular material heated to 130°C, 2 parts by mass of solution (α1) (1 part by mass in terms of pure citric acid) were added, the mixture was stirred for 3 minutes, the sand was removed, and after cooling to room temperature (25°C), it was passed through a sieve with a mesh size of 212 μm, and the material that passed through the sieve was recovered as a coating material (coating sand).

[0054] (Preparation of test pieces) Using a 3D additive manufacturing system (manufactured by 3D Systems, product name "ZPrinter 310 Plus") that employs printing technology, a coating material with a recoater blade mechanism was used to layer the coating material to a thickness of 200 μm on the bottom surface (build table) of a metal case (210 mm long, 260 mm wide, 150 mm high) installed in the 3D additive manufacturing system (process (a)). Next, the print nozzle head was scanned over the layered coating material based on the data obtained from the 3D CAD design of the 3D additive manufacturing object, and the solution (β1) was printed (step (b)). After printing the solution (β1), the build table of the metal case was lowered by one layer (200 μm), and the coating material was layered in the same manner as before (step (a)), and the solution (β1) was printed on top of it (step (b)). Steps (a) and (b) were repeated multiple times. After the final step (b), three hours later, the 3D additively manufactured object was removed from the metal case while still embedded in the coating material powder, and then heat-treated in a dryer at 200°C for one hour (step (c)). After cooling to room temperature (25°C), the coating material from the non-printed areas of the solution (β1) was removed with a brush, and a rectangular prism-shaped 3D additively manufactured object measuring 10 mm in length, 60 mm in width, and 10 mm in height was extracted and used as a test piece. Nine test pieces were produced simultaneously. The bending strength of nine test pieces after cooling was measured, and the average value was calculated. The results are shown in Table 2. Furthermore, using test pieces after measuring their bending strength, the amount of sugar binder added per 100 parts by mass of refractory granular material was determined as follows. The results are shown in Table 2.

[0055] (Calculation of the amount of sugar binder to be added) A test piece was crushed with a file, and 20g of the crushed material was collected in a crucible. The crushed material was dried in the crucible at 105°C for 1 hour to remove moisture, and its weight was measured. Next, the crushed material, after moisture removal, was heat-treated at 800°C for 3 hours. After cooling, the weight of the crushed material was measured, and the loss on ignition of the test piece was calculated using the following formula (1). The results are shown in Table 2. Loss on ignition [%] = (Weight of pulverized material before heating at 800°C [g] - Weight of pulverized material after heating at 800°C [g]) / Weight of pulverized material before heating at 800°C [g] × 100 ... (1)

[0056] Separately, mixed sand was prepared by adding 2.00 parts by mass, 3.00 parts by mass, or 4.00 parts by mass of the same type of solution (β) used to prepare the test piece to 100 parts by mass of the coating material. The resulting mixed sand was heat-treated at 200°C for 1 hour to harden. After cooling, the hardened mixed sand was crushed with a file, and 20 g of the crushed material was collected in a crucible. The crushed material was dried in the crucible at 105°C for 1 hour to remove moisture, and the weight of the crushed material was measured. Next, the crushed material, after moisture removal, was heat-treated at 800°C for 3 hours. After cooling, the weight of the crushed material was measured, and the loss on ignition was calculated using the following formula (2). A calibration curve was created with the loss on ignition on the vertical axis (y) and the amount of solution (β) added on the horizontal axis (x). The results are shown in Figure 1. Loss on ignition [%] = (Weight of pulverized material before heating at 800°C [g] - Weight of pulverized material after heating at 800°C [g]) / Weight of pulverized material before heating at 800°C [g] × 100 ... (2)

[0057] Using the prepared calibration curve, the amount of solution (β) added to 100 parts by mass of coating material in the test piece was determined from the ignition loss of the test piece obtained earlier, and this was converted to the amount of solution (β) added to 100 parts by mass of refractory granular material in the coating material. The results are shown in Table 2. Furthermore, the amount of sugar binder added per 100 parts by mass of refractory granular material was determined from the calculated amount of solution (β) and the concentration of sugar binder in solution (β), and the mass ratio of sugar binder to polycarboxylic acids was determined. The results are shown in Table 2.

[0058] <Examples 1-2 to 1-4> The coating material was prepared in the same manner as in Example 1-1, except that the type of solution (α) shown in Table 2 was used. Test pieces were prepared in the same manner as in Example 1-1, except that the obtained coating material was used and the type of solution (β) shown in Table 2 was used. The bending strength of the obtained test pieces was measured in the same manner as in Example 1-1. The amount of sugar binder added was also determined in the same manner as in Example 1-1. The results are shown in Table 2. Furthermore, the results of the calibration curve created in Example 1-2 are shown in Figure 2, the results of the calibration curve created in Example 1-3 are shown in Figure 3, and the results of the calibration curve created in Example 1-4 are shown in Figure 4.

[0059] <Examples 1-5> (Preparation of sand composition) To 100 parts by mass of refractory granular material heated to 120°C, 0.3 parts by mass of an acid catalyst solution was added and stirred for 3 minutes to evaporate the water used as a solvent. Then, 0.3 parts by mass of zeolite was added and stirred for 1 minute to obtain a sand composition. In the sand composition, the acid catalyst content was 0.18 parts by mass and the zeolite content was 0.3 parts by mass per 100 parts by mass of refractory granular material. In Examples 1-5, amorphous silica (containing 98% by mass of SiO2, product name "SPHERESAND SL SLH#110" manufactured by CHINA MINERAL PROCESSING LIMITED) obtained by flame melting was used as the refractory granular material. As the acid catalyst solution, a mixture of 60 parts by mass of xylene sulfonic acid and 40 parts by mass of water (a 60% by mass acid catalyst solution) was used. As the zeolite, we used Y-type zeolite (product name "HSZ-385HUA" manufactured by Tosoh Corporation, SiO2 / Al2O3 molar ratio = 100, average particle size = 3 μm).

[0060] (Preparation of test pieces) Using a 3D additive manufacturing system employing a printing method (manufactured by C-MET Co., Ltd., product name "Sand Mold Additive Manufacturing System SCM-800"), a sand composition was deposited onto the bottom surface of a metal case installed in the 3D additive manufacturing system using a blade mechanism with a recoater. At this time, the shutter opening angle of the recoater was set to 49.5°. Next, based on the data obtained from 3D CAD design of the shape of the 3D additively manufactured object, the print nozzle head was scanned over the layered sand composition, and an acid-curable binder was printed at a discharge rate of 1.8 parts by mass per 100 parts by mass of sand composition per layer. After printing the acid-curable binder, the bottom surface (build table) of the metal case was lowered by one layer (280 μm), and the sand composition was layered in the same manner as before, and the acid-curable binder was printed on top of it at a discharge rate of 1.8 parts by mass per 100 parts by mass of sand composition per layer. After repeating these layering and printing processes, the sand composition in the areas where the acid-curable binder was not printed was removed with a brush, and a rectangular parallelepiped test piece measuring 10 mm in length, 10 mm in width, and 60 mm in height was obtained. The bending strength of the obtained test pieces was measured. The results are shown in Table 3. Furthermore, a mixture of 89.9 parts by mass of furfuryl alcohol, 10 parts by mass of resorcinol, and 0.2 parts by mass of N-β(aminoethyl)γ-aminopropylmethyldimethoxysilane was used as the acid-curing binder.

[0061] <Example 1-6> A sand composition was prepared in the same manner as in Example 1-5, except that crystalline artificial sand obtained by sintering (containing 95% by mass of Al2O3-SiO2, product name "CB-X#1450" manufactured by Itochu Ceratec Co., Ltd.) was used as the refractory granular material. Using the obtained sand composition, test pieces were manufactured in the same manner as in Example 1-5, except that the amount of acid-curing binder discharged per 100 parts by mass of the sand composition for one layer was changed to 1.6 parts by mass, and the bending strength was measured. The results are shown in Table 3.

[0062] [Table 2]

[0063] [Table 3]

[0064] As is clear from the results in Tables 2 and 3, the test pieces (3D additive manufactured objects) obtained in Examples 1-1 to 1-4 had higher bending strength than the test pieces (3D additive manufactured objects) obtained in Examples 1-5 and 1-6. Furthermore, the test pieces (3D additive manufactured objects) obtained in Examples 1-1 to 1-4 use a coating material in which polycarboxylic acids are coated onto a refractory granular material, and a sugar binder. As a result, even when heated to the pouring temperature, sulfur dioxide gas and other substances are not generated, and the working environment is less likely to deteriorate.

[0065] [Exam 2] As a refractory granular material, artificial sand obtained by the melting method (Ito Kiko Co., Ltd., "Alsand #1000", average particle size 120 μm) was used. Citric acid was used as the polycarboxylic acid. Maltose or maltitol was used as the sugar binder. Maltose and citric acid were mixed in mass ratios of maltose:citric acid = 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100. The resulting mixtures were then dissolved in water to a concentration of 50% by mass, preparing a total of six binder solutions (i). Maltitol and citric acid were mixed in mass ratios of maltitol:citric acid = 100:0, 80:20, 60:40, 40:60, 20:80, and 0:100. The resulting mixtures were then dissolved in water to a concentration of 50% by mass, preparing a total of six binder solutions (ii). Maltose and citric acid were mixed in mass ratios of maltose:citric acid = 80:20, 50:50, and 20:80, and the resulting mixtures were dissolved in water to a concentration of 50% by mass to prepare a total of three types of binder solutions (iii).

[0066] <Examples 2-1 to 2-6> (Preparation of test pieces) 4.00 parts by mass of binder solution (i) was added to 100 parts by mass of refractory granular material, and the mixture was stirred for 1 minute to obtain kneaded sand. The resulting mixed sand was immediately filled into a wooden mold for test piece production, which had six rectangular prisms measuring 10 mm in length, 60 mm in width, and 10 mm in depth, under conditions of 10°C and 20% humidity. The mixture was allowed to harden, and the six test pieces were removed 24 hours after the start of hardening (removal time: 24 hours). The six removed test pieces were heat-treated in a dryer at 150°C or 200°C for 1 hour, and then allowed to cool to room temperature (25°C). The bending strength of six test pieces after cooling was measured, and the average value was calculated. The results are shown in Table 4. Furthermore, water resistance was evaluated using test pieces after the bending strength was measured. The results are shown in Table 4.

[0067] <Examples 2-7 to 2-12> Test pieces were prepared in the same manner as in Examples 2-1 to 2-6, except that binder solution (ii) was used instead of binder solution (i), and various measurements and evaluations were performed. The results are shown in Table 5.

[0068] <Examples 2-13 to 2-15> Test pieces were prepared in the same manner as in Examples 2-1 to 2-6, except that binder solution (iii) was used instead of binder solution (i), and the heat treatment temperature in the dryer was changed to 160°C, 170°C, 180°C, or 190°C. Various measurements and evaluations were then performed. The results are shown in Table 6.

[0069] [Table 4]

[0070] [Table 5]

[0071] [Table 6]

[0072] As is clear from the results in Tables 4-6, it was confirmed that thermal curing of citric acid with maltose or maltitol resulted in higher strength compared to using citric acid alone or maltose or maltitol alone. Furthermore, the strength and water resistance of the test pieces tended to improve with increasing heat treatment temperature. In Test 2, the test pieces were manufactured by filling a wooden mold, but the same trend as in Test 2 was observed when the test pieces were manufactured using 3D additive manufacturing.

[0073] [Exam 3] As a refractory granular material, artificial sand obtained by the melting method (Ito Kiko Co., Ltd., "Alsand #1000", average particle size 120 μm) was used. Citric acid was used as the polycarboxylic acid. Maltitol, sorbitol, or glucose were used as the sugar binder. Maltitol and citric acid were mixed in a mass ratio of maltitol:citric acid = 50:50, and the resulting mixture was dissolved in water to prepare a binder solution (iv) with a concentration of 50% by mass. Sorbitol and citric acid were mixed in a mass ratio of sorbitol:citric acid = 50:50, and the resulting mixture was dissolved in water to prepare a binder solution (v) with a concentration of 50% by mass. Glucose and citric acid were mixed in a mass ratio of glucose:citric acid = 50:50, and the resulting mixture was dissolved in water to prepare a binder solution (vi) with a concentration of 50% by mass.

[0074] <Example 3-1> (Preparation of test pieces) 100 parts by mass of refractory granular material was mixed with 4.00 parts by mass of binder solution (iv) and stirred for 1 minute to obtain kneaded sand. The resulting mixed sand was immediately filled into a wooden mold for test piece production, which had six rectangular prisms measuring 10 mm in length, 60 mm in width, and 10 mm in depth, under conditions of 10°C and 20% humidity. The mixture was allowed to harden, and the six test pieces were removed 24 hours after the start of hardening (removal time: 24 hours). The six removed test pieces were heat-treated in a dryer at 150°C or 200°C for 1 hour, and then allowed to cool to room temperature (25°C). The bending strength of six test pieces after cooling was measured, and the average value was calculated. The results are shown in Table 7. Furthermore, water resistance was evaluated using test pieces after the bending strength was measured. The results are shown in Table 7.

[0075] <Example 3-2> Test pieces were prepared in the same manner as in Example 3-1, except that binder solution (v) was used instead of binder solution (iv), and various measurements and evaluations were performed. The results are shown in Table 7.

[0076] <Example 3-3> Test pieces were prepared in the same manner as in Example 3-1, except that binder solution (vi) was used instead of binder solution (iv), and various measurements and evaluations were performed. The results are shown in Table 7.

[0077] [Table 7]

[0078] As is clear from the results in Table 7, the same results were obtained when sorbitol or glucose was used as the sugar binder as when maltitol was used. In other words, it was confirmed that practical strength can be achieved by thermal curing citric acid and the sugar binder. Furthermore, the strength and water resistance of the test pieces tended to improve with increasing heat treatment temperature. In Test 3, the test pieces were manufactured by filling a wooden mold, but the same trend as in Test 3 was observed when the test pieces were manufactured using 3D additive manufacturing.

[0079] [Exam 4] As the refractory granular material, artificial sand obtained by the melting method (Ito Kiko Co., Ltd., "Alsand #1000", average particle size 120 μm) or silica sand (Mitsubishi Corporation Building Materials Co., Ltd., "Flutary MS-60", average particle size 150 μm) was used. Citric acid was used as the polycarboxylic acid. Maltitol was used as the sugar binder. Maltitol and citric acid were mixed in a mass ratio of maltitol:citric acid = 50:50, and the resulting mixture was dissolved in water to prepare binder solution (vii) with a concentration of 50% by mass.

[0080] <Example 4-1> (Preparation of test pieces) As a fire-resistant granular material, 4.00 parts by mass of binder solution (vii) was added to 100 parts by mass of artificial sand, and the mixture was stirred for 1 minute to obtain kneaded sand. The resulting mixed sand was immediately filled into a wooden mold for test piece production, which had six rectangular prisms measuring 10 mm in length, 60 mm in width, and 10 mm in depth, under conditions of 10°C and 20% humidity. The mixture was allowed to harden, and the six test pieces were removed 24 hours after the start of hardening (removal time: 24 hours). The six removed test pieces were heat-treated in a dryer at 150°C or 200°C for 1 hour, and then allowed to cool to room temperature (25°C). The bending strength of six test pieces after cooling was measured, and the average value was calculated. The results are shown in Table 8. Furthermore, water resistance was evaluated using test pieces after the bending strength was measured. The results are shown in Table 8.

[0081] <Example 4-2> Test pieces were prepared in the same manner as in Example 4-1, except that silica sand was used instead of artificial sand as the refractory granular material, and various measurements and evaluations were performed. The results are shown in Table 8.

[0082] [Table 8]

[0083] As is clear from the results in Table 8, the same results were obtained when silica sand was used as the refractory granular material as when artificial sand was used. In other words, it was confirmed that practical strength can be achieved by thermally curing citric acid and a sugar binder. Furthermore, the strength and water resistance of the test pieces tended to improve with increasing heat treatment temperature. In Test 4, the test pieces were manufactured by filling a wooden mold, but the same trend as in Test 4 was observed when the test pieces were manufactured using 3D additive manufacturing.

Claims

1. The process includes (a) laying out layers of a coating material in which polycarboxylic acids are coated onto a refractory granular material, and (b) injecting a sugar binder into a desired area of ​​the layered coating material. Step (a) and step (b) are repeated until the desired three-dimensional additively fabricated object is fabricated. The aforementioned refractory granular material is not coated with a sulfur-containing acid, and the method is for manufacturing a three-dimensional additively fabricated object.

2. The polycarboxylic acids include at least one of citric acid and malic acid, The method for manufacturing a three-dimensional additively fabricated object according to claim 1, wherein the sugar binder comprises one or more selected from monosaccharides, disaccharides, trisaccharides, and sugar alcohols.

3. A method for manufacturing a three-dimensional additively fabricated object according to claim 1 or 2, further comprising a step (c) of curing the sugar binder by heating, at least after the last step (b).

4. The material comprises a coating material in which polycarboxylic acids are coated onto a refractory granular material, and a sugar binder, each of which is independent of the coating material. The aforementioned refractory granular material is a 3D additive manufacturing kit that is not coated with a sulfur-containing acid.

5. The polycarboxylic acids include at least one of citric acid and malic acid, The 3D additive manufacturing kit according to claim 4, wherein the sugar binder comprises one or more selected from monosaccharides, disaccharides, trisaccharides, and sugar alcohols.

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