JP7267731B2 - Hydraulic composition for additive manufacturing equipment and method for manufacturing mold - Google Patents

Description

TECHNICAL FIELD The present invention relates to a hydraulic composition for additive manufacturing devices (3D printers) excellent in early development of strength, particularly in early development of bending strength, and a method for manufacturing a mold using the composition.

Casting is a traditional metalworking method in which molten metal is poured into molds to produce castings. The self-hardening molds used for this casting are classified into organic and inorganic types depending on the caking material (binder) used. Of these, the inorganic types are mainly classified into water glass type and cement type. However, depending on the casting temperature, the gypsum contained in the cement-based self-hardening mold thermally decomposes to generate gas, which causes defects in the casting and impairs its appearance and function. In addition, the manufacture of this casting mold requires the preparation of models and wooden molds as a pre-process, which is time-consuming and costly.
Therefore, there is a demand for a casting mold manufacturing method that does not impair the appearance of castings and does not require such a pre-process.

By the way, recently, additive manufacturing equipment has attracted attention as a rapid and precise molding means. Among these additional manufacturing devices, for example, a powder lamination forming device is a device that, after spreading powder on a flat surface, sprays a water-based binder onto the powder and solidifies the powder, and then sequentially stacks and forms the solidified products in the vertical direction. is. The feature of this apparatus is that it divides three-dimensional molding data created by three-dimensional CAD or the like into a large number of horizontal planes, and successively stacks the shapes of these horizontal planes to produce a molded body.
Therefore, if the mold can be manufactured using the above-mentioned apparatus, the above-mentioned pre-process becomes unnecessary, and it is expected that the working time and cost can be reduced.

For example, in Patent Document 1, as a hydraulic composition for additive manufacturing equipment suitable for powder lamination molding, refractory sand such as silica sand, olivine sand, and artificial sand is mixed with 15 to 50% of fast-hardening cement and kneaded. A technology is disclosed in which a water-based binder is added to (mixed) materials, solidified and laminated to obtain a molded body. Here, the powder lamination molding method means that the molding liquid is dropped or sprayed through a nozzle such as an inkjet to a predetermined range of the powder material placed on the loading table (pedestal) and solidified, and the layers are solidified one by one. is laminated to form a desired shape.

However, since the molded body produced by the additional manufacturing apparatus using the material described in Patent Document 1 does not have sufficient early strength development, especially bending strength, it is easy to cause defects, and it is difficult to stably supply the product. It may be difficult to manufacture the micro-features that characterize the technology.

Japanese Patent Application Laid-Open No. 2011-51010

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a hydraulic composition for additive manufacturing equipment which is excellent in early strength development.

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention found that a hydraulic composition containing an inorganic binder such as calcium aluminates, polyvinyl alcohol, sand, and water in specific proportions can achieve the above-mentioned objects. I found it and completed the present invention.
That is, the present invention is a hydraulic composition for an addition manufacturing device, etc., having the following constitution.

[1] For 100 parts by mass of the following inorganic binder , 28 to 60 parts by mass of water, and sand Hydraulic composition for addition manufacturing equipment containing 100 to 600 parts by mass of .
[Inorganic binder]
The inorganic binder is 100% by mass of the whole inorganic binder,
50 to 100% by mass of amorphous calcium aluminate having a CaO/Al ₂ O ₃ molar ratio of 1.5 to 3.0, a Blaine specific surface area of 1000 to 6000 cm ² /g, and a vitrification rate of 80% or more. ,
A cement containing 0 to 10% by mass of gypsum in terms of anhydrous gypsum, 0 to 50% by mass of fast-hardening cement, and excluding fast-hardening cement, and having a content of calcium silicate of 25% by mass when the entire cement is 100% by mass. 0 to 50% by mass of cement, which is 0% or more.
[Polyvinyl alcohol]
The polyvinyl alcohol has a saponification degree of 80 to 90 mol%,
The content of polyvinyl alcohol particles larger than 94 μm is 45% by mass or less, and the content of polyvinyl alcohol particles larger than 77 μm is 90% by mass or less.
[2] A method for manufacturing a mold, comprising forming a mold using an addition manufacturing device and the hydraulic composition for an addition manufacturing device according to [1] .
[3] The mold manufacturing method according to [ 2 ] above, wherein the curing temperature of the mold is 10 to 80°C.

The hydraulic composition for additive manufacturing equipment of the present invention has a high early strength development property.

As described above, the present invention provides a hydraulic composition for additive manufacturing equipment (hereinafter referred to as It may be abbreviated as "hydraulic composition".) and the like. Hereinafter, the present invention will be described separately for an inorganic binder, a composite binder, a hydraulic composition, and a method for producing a mold.

1. Inorganic Binder The inorganic binder is a binder containing as an essential component one or more selected from the following calcium aluminates, and further containing gypsum, fast-hardening cement and the like as optional components.
Next, they are divided into calcium aluminates, gypsum, fast-hardening cement, and the like, and explained in detail.

(1) Calcium aluminates The calcium aluminates are 3CaO.Al ₂ O ₃ , 2CaO.Al 2 O ₃ , 12CaO.7Al ₂ O ₃ , 5CaO.3Al ₂ O ₃ , CaO.Al _{2 O 3 and} 3CaO. - calcium aluminates _{such as 5Al2O3} or _{CaO.2Al2O3 ; calcium aluminoferrites such as 2CaO.Al2O3.Fe2O3 or 4CaO.Al2O3.Fe2O3} ; Calcium haloaluminates including calcium fluoroaluminates such as 3CaO.3Al ₂ O ₃ .CaF ₂ and 11CaO.7Al ₂ O ₃ .CaF ₂ in which halogen is dissolved or substituted in aluminate; 8CaO.Na ₂ O.3Al Calcium sodium aluminate such as _2O3 and _{3CaO.2Na2O.5Al2O3 ;} calcium lithium aluminate; _alumina cement _; , S, and other trace elements (including oxides, etc.) are solid-dissolved in minerals.
Among these inorganic binders, calcium aluminate is preferred, and amorphous calcium aluminate is particularly preferred, because it exhibits high strength and generates little gas when used as a mold. Amorphous calcium aluminate is produced by melting a raw material and then quenching it. Therefore, it has substantially no crystalline structure. Since early strength development is high, the vitrification rate is preferably 90% or more.

The CaO/Al ₂ O ₃ molar ratio of the calcium aluminates is preferably 1.5-3.0, more preferably 1.7-2.4. When the molar ratio is 1.5 or more, the hydraulic composition exhibits high early strength, and when it is 3.0 or less, the hydraulic composition has high heat resistance.
In addition, the Blaine specific surface area (fineness specified in JIS R 5201) of calcium aluminates is preferably 1000 to 6000 cm ² /g, more than It is preferably 1500 to 5000 cm ² /g. The Blaine specific surface area of calcium aluminates is more preferably 1,500 to 4,000 cm ² /g, particularly preferably 2,000 cm 2 /g, in order to ensure uniform spreading in the additive manufacturing apparatus and to prevent the strength of the mold from decreasing. ˜3000 cm ² /g.
The content of calcium aluminates in the inorganic binder is preferably 50-100% by mass. When this value is 50% by mass or more, the hydraulic composition exhibits high early strength development and high heat resistance. The value is preferably 60 to 100% by mass, more preferably 70 to 100% by mass, still more preferably 80 to 95% by mass. As described above, among calcium aluminates, amorphous calcium aluminate is preferred.

(2) Gypsum The inorganic binder may further contain gypsum as an optional component in order to further improve early strength development. The gypsum includes one or more selected from anhydrous gypsum, hemihydrate gypsum, and dihydrate gypsum. Among these, gypsum hemihydrate is preferred because of its higher early strength development. The content of gypsum in the inorganic binder is preferably anhydrous, with the total inorganic binder being 100% by mass, in order to improve early strength development and prevent gas generation and graphite spheroidization failure during casting production. It is 0.5 to 10% by mass, more preferably 0.8 to 5% by mass, and still more preferably 1 to 3% by mass in terms of gypsum.
The gypsum may be gypsum contained in cement. Gypsum in cement is generally present in the form of a mixture of gypsum dihydrate and gypsum hemihydrate (mixed gypsum). Since gypsum hemihydrate is produced by dehydrating gypsum dihydrate by heat generated by pulverizing cement, the content ratio of gypsum hemihydrate and gypsum dihydrate fluctuates under the influence of pulverization conditions.

(3) Fast-hardening cement The inorganic binder may contain a fast-hardening cement (ultra fast-hardening cement) as an optional component in order to further improve early strength development, and the fast-hardening cement is preferably JIS R 5210. It is a fast-hardening cement (ultra-fast-hardening cement) whose setting (initial setting) is within 30 minutes, or a water stop cement. Commercially available products such as fast-hardening cement include Super Jet Cement (manufactured by Taiheiyo Cement Co., Ltd.), Jet Cement (manufactured by Sumitomo Osaka Cement Co., Ltd.), Lion Shisui (registered trademark, manufactured by Sumitomo Osaka Cement Co., Ltd.), and Denka Super Cement (Denka company). A fast-hardening cement containing gypsum is preferable because it exhibits high early strength development and facilitates the addition of a small amount of gypsum.
The content of the fast-hardening cement in the inorganic binder is preferably 0 to 50, with the total inorganic binder as 100% by mass, in order to improve early strength development and reduce gas generation when used as a mold. % by mass, more preferably 0 to 30% by mass, still more preferably 5 to 20% by mass.

(4) Other Components in Inorganic Binder The inorganic binder may contain cement as another component (optional component).
The cement preferably sets (first set) within 3 hours and 30 minutes as measured in accordance with JIS R 5210 because it exhibits high early strength development 3 hours after molding, and more preferably within 1 hour.
Cement includes one or more selected from ordinary Portland cement, early-strength Portland cement, moderate heat Portland cement, low heat Portland cement, white Portland cement, ecocement, blast furnace cement, fly ash cement, and cement clinker powder. In the present invention, cement clinker powder is also included in cement. Moreover, the content of calcium silicate in the cement is preferably 25% by mass or more based on 100% by mass of the entire cement. If the content is 25% by mass or more, the strength development after one day of age is high, and if long-term strength development is required, the content is preferably 45% by mass or more.
In order to improve early strength development, the content of cement in the inorganic binder is preferably 0 to 50% by mass, more preferably 0 to 30% by mass, and still more preferably 100% by mass of the entire inorganic binder. 0 to 20% by mass.

2. Composite Binder The composite binder is a binder containing 1.5 to 12 parts by mass of partially saponified polyvinyl alcohol with respect to 100 parts by mass of the inorganic binder. If the mixing ratio of polyvinyl alcohol is less than 1.5 parts by mass, the effect of improving the strength is low. In addition to being unable to manufacture in some cases, there are cases where gas is generated when manufacturing castings, causing defects such as blowholes in castings, and odors at manufacturing sites. The mixing ratio of polyvinyl alcohol is more preferably 2 to 10 parts by mass, more preferably 3 to 9 parts by mass, per 100 parts by mass of the inorganic binder.
The method of pulverizing and mixing the inorganic binder and polyvinyl alcohol includes individual pulverization, in which both are pulverized separately and then mixed, and mixed pulverization, in which both are mixed and then pulverized simultaneously. Mixed pulverization is preferred.
The degree of saponification of the polyvinyl alcohol is preferably 80 to 90 mol % because the solubility is high and the strength of the molded article is improved.
Also, the average particle diameter (median diameter, D50) of polyvinyl alcohol is preferably 150 μm or less, more preferably 90 μm or less, still more preferably 10 to 75 μm, since high strength can be obtained. The content of polyvinyl alcohol particles larger than 94 μm is preferably 90% by mass or less, more preferably 45% by mass or less, and even more preferably 30% by mass or less. Also, the content of polyvinyl alcohol having a diameter of 77 μm or more is preferably 90% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

3. Hydraulic Composition The hydraulic composition is a composition containing 28 to 60 parts by mass of water and sand with respect to a total of 100 parts by mass of the composite binder. If the blending ratio of water is within this range, strength development can be ensured. The mixing ratio of water is preferably 30 to 55 parts by mass, more preferably 35 to 46 parts by mass, from the viewpoint of increasing the strength and dimensional accuracy of the mold.
Also, the blending ratio of sand is preferably 100 to 600 parts by mass, more preferably 150 to 500 parts by mass, and even more preferably 200 to 400 parts by mass with respect to 100 parts by mass of the composite binder. If the blending ratio of sand is within this range, it is also possible to ensure strength development.
The sand is not particularly limited as long as it is refractory sand, and examples include one or more selected from silica sand, olivine sand, zircon sand, chromite sand, alumina sand, artificial sand, and the like. As the water, ordinary tap water, well water, or the like can be used. In addition, since water imparts various functions required, one or more selected from thickeners, lubricants, fluidizing agents, surfactants, and surface tension reducing agents may be mixed and used. good.

4. Other Components in the Hydraulic Composition In order to facilitate the work of removing the uncured powder of the hydraulic composition remaining after molding from the molded body (depowder), the hydraulic composition of the present invention further comprises As an optional component, 0.1 to 2 parts by weight, more preferably 0.5 to 1.5 parts by weight of hydrophobic fumed silica can be included with respect to a total of 100 parts by weight of the composite binder. Here, hydrophobic fumed silica is silica powder obtained by treating the surface of fumed silica with silane or siloxane to make the surface hydrophobic.
Further, the BET specific surface area of the hydrophobic fumed silica is preferably 30 to 300 m ² /g in order to further increase the removal efficiency of the powder of the hydraulic composition. If the BET specific surface area of the hydrophobic fumed silica is within this range, the fluidity of the powder is improved, the surface spread by the additional manufacturing device is flat, and the weight of the mold can be reduced without lowering the strength. . Hydrophobic fumed silica is also effective in preventing caking of powder and improving mixability.

The hydraulic composition of the present invention may further contain arbitrary components such as blast furnace slag, fly ash, silica fume, silica fine powder, and limestone powder as strength development modifiers.

5. Manufacturing Method of Casting Mold This manufacturing method is a method of manufacturing a casting mold using an additive manufacturing apparatus and the hydraulic composition of the present invention. The additive manufacturing device is not particularly limited, and a commercially available product such as a powder lamination type additive manufacturing device can be used. Alternatively, the pre-water-containing hydraulic composition is prepared by mixing the aforementioned ingredients in a commercial mixer or by hand. When a plurality of materials are used as the binding material, the binding materials may be mixed in advance using a commercially available mixer or manually, or may be mixed and pulverized using a pulverizer.
Methods for curing the mold include air curing alone, air curing followed by water curing, and surface impregnation curing. Among these, air curing alone is preferable from the viewpoint of early development of strength and suppression of water vapor generated during casting production. The temperature for air curing is preferably 10 to 100°C, more preferably 30 to 80°C, from the viewpoint of strength enhancement by calcium aluminate, cement and polyvinyl alcohol. The relative humidity in air curing is preferably 10 to 90%, more preferably 15 to 80%, still more preferably 20 to 60% from the viewpoint of sufficient strength development and production efficiency. Furthermore, the air curing time is preferably 1 hour to 1 week, more preferably 2 hours to 5 days, still more preferably 3 hours to 4 days, from the viewpoint of sufficient strength development and production efficiency.

EXAMPLES The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples.
1. Materials used (1) Calcium aluminates
(i) amorphous calcium aluminate (abbreviation: CA)
The CaO/Al ₂ O ₃ molar ratio is 2.2, the vitrification rate is 95% or more, and the Blaine specific surface area is 2040 cm ² /g.
(ii) Alumina cement (abbreviation: AC)
Denka Alumina Cement No. 1 (trade name), Blaine specific surface area: 4570 cm ² /g, manufactured by Denka.
(2) Rapid hardening cement
(i) Super Jet Cement (trade name), calcium silicate content of 47% by mass, initial setting of 30 minutes, Blaine specific surface area of 4700 cm ² /g. However, it contains 14% by mass of anhydrous gypsum. Manufactured by Taiheiyo Cement.
(ii) Water stop cement Lion Shisui 105 (trade name) manufactured by Sumitomo Osaka Cement Co., Ltd.
(3) Early Strength Portland Cement Calcium silicate content of 75% by mass, initial setting of 30 minutes, Blaine specific surface area of 4000 cm ² /g, manufactured by Taiheiyo Cement Co., Ltd.
(4) Gypsum Natural anhydrous gypsum produced in Thailand with Blaine specific surface area of 7200 cm ² /g.
(5) Sand Equal amounts of the following two types of artificial foundry sand were mixed and used.
Espearl #180L (trade name), alumina type, manufactured by Yamakawa Sangyo Co., Ltd.
Naigai Cerabeads #1450 (registered trademark), alumina-based, manufactured by Itochu Ceratec.
(6) Polyvinyl alcohol (i) Polyvinyl alcohol a
Product number 22-88S1 (PVA217SS), manufactured by Kuraray Co., Ltd.
The degree of saponification is 87-89%, the average particle diameter (median diameter, D50) is 60 μm, the content of particles larger than 94 μm is 29% by mass, and the content of particles larger than 77 μm is 47% by mass, and 10% The diameter (D10) is 25 μm and the 90% diameter (D90) is 121 μm.
[Classification of Polyvinyl Alcohol]
Polyvinyl alcohol a is classified using a sieve, and the openings are between 75 μm and 150 μm (average particle size 106 μm), between 45 μm and 75 μm (average particle size 63 μm), and between 25 μm and 45 μm (average particle size). A classified product of polyvinyl alcohol having an average particle size of 38 μm was produced.
Furthermore, a pulverized product of polyvinyl alcohol a was also prepared by mixing calcium aluminate and polyvinyl alcohol a, which had been coarsely pulverized to a particle size of 5 mm or less, and pulverizing the calcium aluminate at the same time so that the Blaine specific surface area of the calcium aluminate was 2040 cm ² /g. bottom. However, the particle size of the pulverized product of polyvinyl alcohol a was mixed with calcium aluminate and could not be measured. However, the average particle diameter (median diameter, D50) of calcium aluminate having a Blaine specific surface area of 2040 cm ² /g is 25 μm, which is presumed to be smaller than 25 μm considering the crushability.
(ii) polyvinyl alcohol b
Product number KP18-88S1, manufactured by Kuraray Co., Ltd.
The degree of saponification is 87-89%, the average particle diameter (median diameter, D50) is 57 μm, the content of particles larger than 94 μm is 30% by mass, and the content of particles larger than 77 μm is 44% by mass, and 10% The diameter (D10) is 23 μm and the 90% diameter (D90) is 123 μm.
(iii) polyvinyl alcohol c
Product number 22-88 S1 (PVA217S), manufactured by Kuraray.
The degree of saponification is 87-89%, the average particle size (median diameter, D50) is 113 μm, the content of particles larger than 94 μm is 81% by mass, and the content of particles larger than 77 μm is 87% by mass, and 10% The diameter (D10) is 57 μm and the 90% diameter (D90) is 162 μm.
(iv) polyvinyl alcohol d
Product number D5100, manufactured by Nippon Synthetic Chemical Co., Ltd.
The degree of saponification is 87-89%, the average particle diameter (median diameter, D50) is 56 μm, the content of particles larger than 94 μm is 38% by mass, and the amount of particles larger than 77 μm is 46% by mass. D10) is 14 μm and 90% diameter (D90) is 155 μm.
(v) Polyvinyl alcohol e
Product No. Elvanol 71-30, manufactured by Kuraray.
The degree of saponification is 100%, and the average particle diameter (median diameter, D50) is 110 μm.
(vi) Polyvinyl alcohol f
Part No. Elvano 80-18, manufactured by Kuraray.
The degree of saponification is 100%, and the average particle diameter (median diameter, D50) is 98 μm.
The particle size of the polyvinyl alcohol was measured by SALD-2000J manufactured by Shimadzu Corporation using silicone oil as a medium.
(7) Water 3 mass% glycerol aqueous solution (binder solution for ProJet660Pro), manufactured by 3D System

2. Preparation of Hydraulic Composition and Specimen The specimens of Examples 1 to 4 and Comparative Examples 1 to 5 were made of the amorphous calcium aluminate (CA), mineral fine powder (Blaine specific surface area of 2000 cm ² /g Silica stone powder), Super Jet cement, unclassified polyvinyl alcohol, and sand were mixed in the amounts shown in Table 1 to prepare a powder mixture (hydraulic composition containing no water).
Next, using the powder mixture and a binder injection type powder laminate molding device (trade name: ProJet660Pro manufactured by 3D System Co., Ltd.) as an additional manufacturing device, a binder injection method is performed to obtain a cross-sectional dimension of 10 mm long and 16 mm wide. , and a molded body having a length of 80 mm. The molding conditions were as follows: the water volume setting of the device was 65% outside (Shell) and 90% inside (Core) (water/composite binder ratio was 29 to 32% by mass), room temperature (20°C), relative humidity 60%. %Met. Further, the compact was air-cured for 3 hours under the conditions of 40° C. and 30% relative humidity to prepare a test piece.
The specimens of Examples 5 to 28 were prepared by mixing 90 parts by mass of the amorphous calcium aluminate, 10 parts by mass of super jet cement, polyvinyl alcohol in the amounts shown in Table 2, and 200 parts by mass of sand. A mixture (hydraulic composition containing no water) was prepared. Next, under the conditions of room temperature (20° C.) and relative humidity of 60%, the binder injection method was performed with the set water amount and the water/composite binder ratio of the apparatus shown in Table 2, so that the cross-sectional dimension was 10 mm in length. A compact having a width of 16 mm and a length of 80 mm was produced. Further, the molded body was air-cured for 3 hours at 20° C., 40° C. or 60° C. and a relative humidity of 30% to prepare a test piece.
In addition, in the production of the molded body by the above apparatus, a predetermined position of the powder mixture is selected, the water amount setting value of the apparatus is adjusted from the nozzle, and water is sprayed to the outside and inside of the powder mixture. The mixture solidified.

3. Measurement of bending strength of specimen Next, using the specimen, a three-point bending test is performed with a bending strength tester (model number: MODEL-2257, manufactured by Aikoh Engineering Co., Ltd.). The width and height dimensions of were measured. The results are shown in Tables 1-3 . From the viewpoint of practicality, a bending strength of 1.0 N/mm ² or more at a material age of 3 hours was taken as a target value (practical).
As shown in Table 1, the specimen (Comparative Example 4) made only from calcium aluminates does not meet the standard values. Also, the specimens containing completely saponified polyvinyl alcohol (Comparative Examples 2 and 3) do not satisfy the standard value, but the specimens containing partially saponified polyvinyl alcohol (Examples 1 to 4) satisfy the standard value.

4. Preparation of hydraulic composition and test piece According to the formulation in Table 3, calcium aluminates, cement, gypsum, polyvinyl alcohol a, and sand are mixed to form a powder mixture (hydraulic composition containing no water). made.
Next, using the powder mixture and a binder injection type powder additive manufacturing device (trade name: ProJet660Pro manufactured by 3D System Co., Ltd.) as an additional manufacturing device, the cross-sectional dimensions are 10 mm long and 16 mm wide by a binder injection method. , and a length of 80 mm, the molded body was air-cured under conditions of 40° C. and a relative humidity of 30% for 3 to 72 hours to prepare a test piece.
In addition, in the production of the molded body by the above apparatus, a predetermined position of the powder mixture is selected, and water is sprayed from the nozzle to the outside and inside of the test piece according to the water amount setting value of the apparatus shown in Table 3, and the powder The mixture solidified.

5. Bending Strength of Specimen Next, a three-point bending test was performed using the specimen and a bending strength tester (model number: MODEL-2257, manufactured by Aikoh Engineering Co., Ltd.) to measure the bending strength of the specimen. Table 3 shows the results. From the viewpoint of practicality, a bending strength of 1.0 N/mm ² or more at a material age of 3 hours was taken as a target value (practical).
As shown in Table 3, the flexural strengths of all examples satisfy the above reference value. In addition, the strength of the specimens (Examples 29 to 37) in which quick-hardening cement and gypsum were mixed with calcium aluminates was higher than that of the specimens containing calcium aluminates and partially saponified polyvinyl alcohol (Example 1). is expensive. Among calcium aluminates, the specimen containing amorphous calcium aluminate (Example 32) has higher strength than the specimen containing alumina cement (Example 33).

Claims (3)

For 100 parts by mass of the following inorganic binder , for a total of 100 parts by mass of the composite binder containing 1.5 to 12 parts by mass of the following polyvinyl alcohol , 28 to 60 parts by mass of water and 100 to 100 parts by mass of sand 600 parts by mass of hydraulic composition for addition manufacturing equipment.
[Inorganic binder]
The inorganic binder is 100% by mass of the whole inorganic binder,
50 to 100% by mass of amorphous calcium aluminate having a CaO/Al ₂ O ₃ molar ratio of 1.5 to 3.0, a Blaine specific surface area of 1000 to 6000 cm ² /g, and a vitrification rate of 80% or more. ,
A cement containing 0 to 10% by mass of gypsum in terms of anhydrous gypsum, 0 to 50% by mass of fast-hardening cement, and excluding fast-hardening cement, and having a content of calcium silicate of 25% by mass when the entire cement is 100% by mass. 0 to 50% by mass of cement, which is 0% or more.
[Polyvinyl alcohol]
The polyvinyl alcohol has a saponification degree of 80 to 90 mol%,
The content of polyvinyl alcohol particles larger than 94 μm is 45% by mass or less, and the content of polyvinyl alcohol particles larger than 77 μm is 90% by mass or less. A method for manufacturing a mold, comprising forming a mold using an additive manufacturing device and the hydraulic composition for an additive manufacturing device according to claim 1 . The mold manufacturing method according to claim 2 , wherein the curing temperature of the mold is 10 to 80°C.