JP7330697B2 - 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), which is excellent in early strength development and dimensional stability, 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 blended 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 (form) a desired shape.

However, the molded body produced by the additional manufacturing apparatus using the material described in Patent Document 1 is prone to defects because the early strength development, especially the bending strength, is not sufficient, so it is difficult to stably supply the product. In some cases, it is difficult to manufacture finely shaped products that are characteristic of molding technology.
In addition, when dimensional changes such as shrinkage and expansion occur after molding, cracks and splits may occur. Furthermore, if the dimensions of the molded body such as the manufactured mold are different, it becomes necessary to adjust the dimensions of the molded body.

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 use in additive manufacturing equipment, which is excellent in early development of bending strength and dimensional stability.

As a result of intensive studies to solve the above problems, the inventors of the present invention have found a hydraulic composition containing an inorganic binder such as calcium aluminates, polyvinyl alcohol having a specific average particle size, sand, and a specific amount of water. found that the above object can be achieved, 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, for a total of 100 parts by mass of the composite binder containing 2 to 12 parts by mass of polyvinyl alcohol, 28 to 60 parts by mass of water and 100 parts by mass of sand Hydraulic composition for addition manufacturing equipment containing up to 600 parts by mass.
[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 degree of saponification of 80 to 90 mol % and an average particle size (D50) of 57 to 106 μm.
[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.

ADVANTAGE OF THE INVENTION The hydraulic composition for additive manufacturing devices of the present invention has high early strength development and high dimensional stability, is easy to depowder, and is capable of blowing out powder from the molded body, peeling the molded body, and removing water from the molded body. No bleeding.

As described above, the present invention provides a hydraulic composition for additive manufacturing equipment, which contains a composite binder containing 2 to 12 parts by mass of polyvinyl alcohol having an average particle size of 110 μm or less, and sand with respect to 100 parts by mass of an inorganic binder. (hereinafter sometimes 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, quick-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 to 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 calculated as 100% by mass of the inorganic binder in order to improve early strength development and prevent gas generation and graphite spheroidization failure during casting production. , preferably 0.5 to 10% by mass, more preferably 0.8 to 5% by mass, and even more preferably 1 to 3% by mass.
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 for further improvement of early strength development, and is preferably measured in accordance with JIS R 5210. It is a fast-hardening cement (ultra-fast-hardening cement) that sets (initial setting) 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). Among them, gypsum-containing rapid-hardening cement is preferable because it has 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 according to 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.
The content of cement in the inorganic binder is preferably 0 to 50% by mass, more preferably 0 to 30% by mass, more preferably 0 to 30% by mass, based on 100% by mass of the entire inorganic binder, in order to improve early strength development. 0 to 20% by mass.

2. Composite Binder The composite binder is a binder containing 2 to 12 parts by mass of polyvinyl alcohol with respect to 100 parts by mass of the inorganic binder. If the content of polyvinyl alcohol is less than 2 parts by mass, the effect of improving the strength is low, and if it exceeds 12 parts by mass, deformation and cracking may occur due to shrinkage of the molded product depending on the shape, making it impossible to manufacture a mold with a complicated shape. In addition, there are cases in which gas is generated when manufacturing castings, causing defects such as blowholes in castings, and odors at manufacturing sites. The content of polyvinyl alcohol is more preferably 2 to 10 parts by mass, still more preferably 3 to 9 parts by mass, per 100 parts by mass of the inorganic binder.
The saponification degree of the polyvinyl alcohol is preferably 80 to 90 mol % because of its high solubility and high strength.
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.
Further, the average particle diameter (median diameter, D50) of polyvinyl alcohol is 110 μm or less, more preferably 90 μm or less, further preferably 10 to 75 μm, since high strength can be obtained. The content of polyvinyl alcohol particles larger than 94 μm is preferably 80% by mass or less, more preferably 45% by mass or less, and even more preferably 30% by mass or less. The content of polyvinyl alcohol particles larger than 77 μm is preferably 80% 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 42 parts by mass, more preferably 32 to 40 parts by mass, from the viewpoint of increasing the strength and dimensional accuracy of the mold.
Also, the mixing 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 , 0.1 to 2.0 parts by weight, more preferably 0.5 to 1.5 parts by weight of hydrophobic fumed silica can be included as an optional component 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 optional components such as blast furnace slag, fly ash, silica fume, silica fine powder, and limestone powder as strength development modifiers.

5. Manufacturing Method of Mold This manufacturing method is a method of manufacturing a 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 of 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, quick-hardening cement, polyvinyl alcohol, and the like. 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.
Alumina-based, trade name Espearl #180L, manufactured by Yamakawa Sangyo Co., Ltd.
Alumina-based, trade name: Naigai Cerabeads #1450 (registered trademark), manufactured by Itochu Ceratec.
(6) Polyvinyl alcohol (i) Polyvinyl alcohol a
Product number 22-88S1 (PVA217SS), manufactured by Kuraray Co., Ltd.
The saponification degree is 87 to 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 opening is between 75 μm and 150 μm (average particle size 106 μm, corresponding to “a106” in Table 1), and the opening is between 45 μm and 75 μm (average particle size 63 μm , corresponding to "a63" in Table 1), and classified products of polyvinyl alcohol having an opening between 25 μm and 45 μm (average particle diameter of 38 μm, corresponding to "a38" in Table 1).
Furthermore, calcium aluminate coarsely ground to a particle size of 5 mm or less and polyvinyl alcohol a were mixed and simultaneously pulverized so that the Brane specific surface area of calcium aluminate was 2040 cm ² /g. "X" in 1.) was also produced. 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 finer than 25 μm in consideration of the grindability.
(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.
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% by mass glycerol aqueous solution (binder solution for ProJet660Pro), manufactured by 3D System.

2. Hydraulic composition and preparation of test specimen 90 parts by mass of the amorphous calcium aluminate (CA), 10 parts by mass of super jet cement, polyvinyl alcohol in the amount shown in Table 1, and sand are mixed to form a powder mixture (Hydraulic composition containing no water) was prepared.
Next, using the hydraulic composition and a binder injection type powder laminate molding device (trade name: ProJet660Pro manufactured by 3D System Co., Ltd.) as an additional manufacturing device, under the conditions of room temperature (20 ° C.) and relative humidity of 60%. , a molded article having cross-sectional dimensions of 10 mm long, 16 mm wide, and 80 mm long was produced by the binder injection method. This compact was air-cured for 3 to 72 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 flexural strength and dimensions of test piece The width and height dimensions of the specimen were measured. Table 1 shows the results. From the viewpoint of practicality, the target values are bending strength of 1.0 N/mm ² or more at 3 hours of age, 1.8 N/mm ² or more within 3 days of age, and dimensional stability of 100 ± 5%. range was set as pass (practical).
As shown in Table 1, the examples satisfy the standard values for both the bending strength and the dimensional stability, but the comparative examples satisfy the standard values for either or neither of the bending strength and the dimensional stability.

4. Preparation of hydraulic composition and test piece According to the formulation in Table 2, 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 hydraulic composition and a binder injection type powder laminate molding device (trade name: ProJet660Pro manufactured by 3D System Co., Ltd.) as an additional manufacturing device, under the conditions of room temperature (20 ° C.) and relative humidity of 60%. , a molded article having cross-sectional dimensions of 10 mm long, 16 mm wide, and 80 mm long was produced by the binder injection method. This compact was air-cured for 3 to 72 hours under the conditions of 40° C. and 30% relative humidity 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.

5. Measurement of flexural strength and dimensions of test piece The width and height dimensions of the specimen were measured. The results are shown in Tables 1 and 2 . From the viewpoint of practicality, the target values are bending strength of 1.0 N/mm ² or more at 3 hours of age, 1.8 N/mm ² or more within 3 days of age, and dimensional stability of 100 ± 5%. range was set as pass (practical).
As shown in Tables 1 and 2, all examples satisfy the criteria for both bending strength and dimensional stability. In addition, in all examples, depowder is easy, powder is not blown out from the apparatus, and there is no peeling or bleeding of the specimen.

Claims (3)

100 parts by mass of the following inorganic binder, 28 to 60 parts by mass of water, and 100 to 600 parts by mass of sand for a total of 100 parts by mass of the composite binder containing 2 to 12 parts by mass of the following polyvinyl alcohol Hydraulic composition for additive manufacturing equipment containing part.
[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 degree of saponification of 80 to 90 mol % and an average particle size (D50) of 57 to 106 μm. 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.