JP7610438B2 - Method for improving strength of a molded object and method for manufacturing a reinforced molded object - Google Patents

Description

The present invention relates to a method for improving the strength of objects containing oxides, and a method for producing reinforced objects with improved strength.

Casting is a traditional metal processing method in which molten metal is poured into a mold to produce castings. The hardening molds used in this casting can be organic or inorganic, depending on the binder (caking agent) used; of these, the inorganic types are mainly water glass-based and cement-based. However, with cement-based self-hardening molds, depending on the pouring temperature of the metal, the gypsum contained in the binder can thermally decompose, generating gas, causing defects in the casting and impairing its aesthetics and functionality. In addition, the production of this mold requires the creation of a model or wooden pattern as a pre-process, but this pre-process is time-consuming and costly. Therefore, a method of manufacturing a mold that does not impair the aesthetics of the casting and does not require the above-mentioned pre-process is desired.

Meanwhile, in recent years, additive manufacturing equipment has been attracting attention as a rapid and precise molding method. For example, one type of additive manufacturing equipment is a powder lamination molding equipment, which spreads powder on a flat surface, sprays an aqueous binder onto the powder, and then molds the hardened powder by stacking it vertically in layers. The feature of this equipment is that it divides the data of a three-dimensional molded body created using 3D CAD or the like into multiple horizontal planes, and the shapes of these horizontal planes are stacked in layers to produce a molded body. If molded bodies can be manufactured using the above equipment, the above pre-processing steps will be unnecessary, which could reduce work time and costs.

For example, a technology has been proposed for obtaining a compact by mixing refractory sand such as silica sand, olivine sand, and artificial sand with 15 to 50% fast-hardening cement as a hydraulic composition suitable for the binder jetting method (powder laminate molding method) and adding an aqueous binder to the mixture, which is then solidified and laminated (see, for example, Patent Document 1). Here, the binder jetting method is a method in which a molding liquid is dripped or sprayed through a nozzle such as an inkjet onto a specified area of powder material placed on a loading platform (pedestal) to solidify it, and the solidified layers are successively laminated to form the desired shape.

However, molded bodies made using the above materials are prone to chipping due to insufficient early strength development, especially bending strength, and it can be difficult to impart fine shapes, which are a feature of molding technology using additive manufacturing equipment, or to steadily supply products with fine shapes. In addition, when molded bodies of complex shapes such as casting molds are manufactured using the above materials, cracks may occur if dimensional changes such as shrinkage or expansion occur after manufacturing, and if the dimensions of the molded body differ, work to adjust the dimensions is necessary. Furthermore, it is desirable to be able to easily remove the unhardened powder of hydraulic composition remaining after molding from the molded body (de-powdering).

A method has also been proposed in which an additive manufacturing object is manufactured using an additive manufacturing powder containing a ceramic powder and a binder, and then the additive manufacturing object is fired at a high temperature (see, for example, Patent Document 2). The proposal states that the method produces an additive manufacturing object that has appropriate core strength and other fired physical and chemical properties.

However, even the above techniques are insufficient to fully satisfy recent requirements for the mechanical strength of additive manufacturing products, such as bending strength of 10 MPa or more, and there is still room for improvement.

JP 2011-51010 A JP 2015-226935 A

In light of these circumstances, the present invention aims to provide a method for improving the strength of a molded object.

Another object of the present invention is to provide a method for manufacturing reinforced objects with improved strength.

As a result of extensive research, the inventors have discovered the following new methods for improving the strength of a molded object and for manufacturing a reinforced molded object, and have found that the above-mentioned objects can be achieved by each of the above methods, thus completing the present invention.

That is, the present invention includes the following aspects:

Item 1. A step (1) of impregnating a shaped object containing an oxide containing at least one element selected from the group consisting of Si, Al, Ca, Zr, Ti, Fe, Cr, and Mg with at least one silica-containing liquid containing a silica sol solution or an alkyl silicate solution;
A step (2) of subjecting the shaped object treated in the step (1) to a heat treatment at 800° C. or higher;
A step (3) of impregnating the shaped object treated in the step (2) with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution; and
The method includes a step (4) of subjecting the shaped object treated in the step (3) to a heat treatment at 800° C. or higher,
A method for improving the strength of a shaped object, wherein at least one of the steps (2) and (4) is a heat treatment at 1000° C. or higher.

Item 2. The method for improving the strength of a molded object according to Item 1, wherein the molded object is manufactured by an additive manufacturing device.

Item 3. The strength improvement method according to item 1 or 2, wherein the shaped object contains 50% by mass or more of the oxide relative to the entire shaped object.

Item 4. The strength improvement method according to any one of items 1 to 3, in which the impregnation treatment in step (1) is carried out for 5 to 120 seconds.

Item 5. The strength improvement method according to any one of items 1 to 4, wherein the alkyl silicate in the alkyl silicate solution is a dimer or higher alkyl silicate.

Item 6. The strength improvement method according to any one of items 1 to 4, wherein the alkyl silicate in the alkyl silicate solution is an alkyl silicate having a pentamer or more.

Item 7. The strength improvement method according to any one of items 1 to 6, wherein the heat treatment in step (2) is at 2000°C or less.

Item 8. The strength improvement method according to any one of items 1 to 7, wherein the heat treatment in step (4) is at 2000°C or less.

Item 9. Furthermore,
A step (5) of impregnating the shaped object treated in the step (4) with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution; and
9. The strength improving method according to any one of items 1 to 8, further comprising a step (6) of subjecting the shaped object treated in the step (5) to a heat treatment at 800° C. or higher.

Item 10. The strength improvement method according to Item 9, wherein the heat treatment in step (6) is at 2000°C or less.

Item 11. The strength improvement method according to any one of items 1 to 10, in which the shaped object is used as a casting mold.

Item 12. A step (1) of impregnating a shaped object containing an oxide containing at least one element selected from the group consisting of Si, Al, Ca, Zr, Ti, Fe, Cr, and Mg with at least one silica-containing liquid containing a silica sol solution or an alkyl silicate solution;
A step (2) of subjecting the shaped object treated in the step (1) to a heat treatment at 800° C. or higher;
A step (3) of impregnating the shaped object treated in the step (2) with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution; and
The method includes a step (4) of subjecting the shaped object treated in the step (3) to a heat treatment at 800° C. or higher,
A method for producing a reinforced object, wherein at least one of the steps (2) and (4) is a heat treatment at 1000°C or higher.

By using the method for improving the strength of a molded object of the present invention, it is possible to improve the strength, dimensional stability, and gas generation during heating of the molded object.

In addition, by using the method for manufacturing reinforced objects of the present invention, it is possible to easily and reliably obtain objects that have high strength, good dimensional stability, and suppressed gas generation when heated.

FIG. 1 is a graph showing the evaluation results of a three-point bending strength test in the examples. FIG. 2 is a graph showing the evaluation results of the three-point bending strength test in the examples. FIG. 3 is a graph showing the evaluation results of the three-point bending strength test in the examples.

The following describes in detail the embodiments of the present invention, but the present invention is not limited to these embodiments.

＜Sculpture＞
The shaped article in the present invention contains an oxide containing at least one element selected from the group consisting of Si, Al, Ca, Zr, Ti, Fe, Cr, and Mg.

The above-mentioned object can be formed, for example, using a powder for forming containing particles containing the above-mentioned oxide (hereinafter also referred to as base material particles). For example, a powder for forming containing base material particles and an adhesive component is prepared, and a model (layered model, etc.) is formed using this powder for forming (powder for layered modeling, etc.). The base material particles may be particles that undergo a hydration reaction (typically the generation of hydrates or hydroxides) when water comes into contact with the particles, or particles that do not undergo a hydration reaction, or even if they do, they may be limited to a microscopic range on the surface of the particles, or a mixture of these. The base material particles are components that constitute the base material of the object to be formed. In addition, the oxide containing at least one element selected from the group consisting of Si, Al, Ca, Zr, Ti, Fe, Cr, and Mg contained in the object is not limited to being contained in the base material particles, and the oxide may be added or mixed into the powder for forming.

The oxide is not particularly limited, and examples thereof include calcium aluminate (Ca-Al-O), calcium silicate (Ca-Si-O), mullite (Al-Si-O), Al ₂ O ₃ , ZrO ₂ , ZrSiO ₄ , SiO ₂ , Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , chromite (Cr-Fe-Mg-O), olivine (Mg-Fe-Si-O), spinel (MgAl ₂ O ₄ ), TiO _2, etc. These may be used alone or in combination of two or more.

There are no particular limitations on the material or properties of the base particles, so long as they contain the oxide. For example, the base particles may be inorganic particles such as zirconium silicate, mullite, alumina, blast furnace slag, fly ash, silica fume, hydrophobic fumed silica, sand, rapid hardening cement, cement, and silica fine powder, organic particles, and organic-inorganic composite particles.

The shape of the base material particles may be, for example, spherical, elliptical, non-spherical, etc. The average particle size of the base material particles is not particularly limited, but may be, for example, 1 μm or more and 200 μm or less. From the viewpoint of moldability, the average particle size of the base material particles may be, for example, 5 μm or more, 10 μm or more, 20 μm or more, 30 μm or more, or 40 μm or more. In addition, the average particle size of the base material particles may be, for example, 200 μm or less, 140 μm or less, 120 μm or less, 100 μm or less, or 80 μm or less.

In this specification, unless otherwise specified, "average particle size" refers to the particle size at 50% of the cumulative value in the particle size distribution measured using a particle size distribution measuring device based on the laser scattering/diffraction method, i.e., the 50% volume average particle size (D50 size).

The content of the base material particles in the powder for modeling is not particularly limited. The content of the base material particles can be, for example, 60 parts by mass or more, 70 parts by mass or more, 80 parts by mass or more, 85 parts by mass or more, 90 parts by mass or more, and, for example, 99 parts by mass or less, 98 parts by mass or less, 97 parts by mass or less, per 100 parts by mass of the total amount of the powder for layered modeling.

The sand used as the base material particles is not particularly limited as long as it is fireproof sand, and examples of the sand include one or more types selected from silica sand, olivine sand, zircon sand, chromite sand, alumina sand, and artificial sand.

The above rapid-setting cement as the base particles can be included as an optional component to further improve early strength development. The above rapid-setting cement is preferably a rapid-setting cement whose initial setting time measured in accordance with JIS R 5210 is within 30 minutes, or a water-stopping cement. Examples of commercially available products such as rapid-setting cement include Super Jet Cement (manufactured by Taiheiyo Cement Corporation), Jet Cement (manufactured by Sumitomo Osaka Cement Co., Ltd.), Lion Shisui (registered trademark, manufactured by Sumitomo Osaka Cement Co., Ltd.), and Denka Super Cement (manufactured by Denka Co., Ltd.). Among these, rapid-setting cement containing gypsum is preferred because the inclusion of a small amount of gypsum improves early strength development.

The content of the rapid hardening cement is preferably 0 to 50% by mass, more preferably 0 to 30% by mass, and even more preferably 5 to 20% by mass, based on 100% by mass of the total solid content of the molding liquid, in order to improve early strength development and reduce gas generation when used as a mold, etc.

The above-mentioned cement as the base material particles can be included as an optional component. If the initial setting of the above-mentioned cement measured in accordance with JIS R 5210 is within 3 hours and 30 minutes, it is preferable because the early strength development 3 hours after molding is high, and it is more preferable that the initial setting of the cement is within 1 hour. The content of the cement in the above-mentioned molding liquid is preferably 0 to 50% by mass, more preferably 0 to 30% by mass, and even more preferably 0 to 20% by mass, based on the total solid content of the above-mentioned molding liquid as 100% by mass, in order to improve the early strength development.

The above cement may be one or more selected from ordinary Portland cement, high-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 the term cement.

The calcium silicate content in the cement is preferably 25% by mass or more, with the entire cement being 100% by mass. If the content is 25% by mass or more, the strength development is high even after one day of age. If long-term strength development is required, the content is preferably 45% by mass or more.

The adhesive components include water-soluble adhesive components and water-insoluble adhesive components. Examples of water-soluble adhesive components include water-soluble adhesive components mainly composed of thermoplastic resins, thermosetting resins, polysaccharides, etc. These may be used alone or in combination of two or more. In this specification, the water-soluble adhesive component refers to resin particles that, when 2 parts by mass of the adhesive component are added to 100 parts by mass of water at a liquid temperature of 90°C and stirred for 4 hours, all or part of the adhesive component dissolves, and the aqueous solution in which the adhesive component is dissolved exhibits a higher viscosity than water. The water-soluble adhesive component is a component that dissolves in water when mixed with a modeling liquid containing water and bonds base material particles together, etc.

In addition, in this specification, being mainly composed means that the proportion of the above substance in the entire composition (purity of the above substance) is 50% or more by mass, preferably 90% or more, 95% or more, 97% or more, 98% or more, or 99% or more.

Examples of the thermoplastic resin include vinyl alcohol resin (PVA), isobutylene resin, polyamide resin, polyester resin, etc.

The vinyl alcohol resin is a resin containing vinyl alcohol units as the main repeating units. In the resin, the ratio of the number of moles of vinyl alcohol units to the number of moles of all repeating units is usually 50% or more, and may be 65% or more, 75% or more, or 85% or more. All repeating units may be substantially composed of vinyl alcohol units. The type of repeating unit other than the vinyl alcohol unit in the vinyl alcohol resin is not particularly limited, and may be, for example, a vinyl acetate unit.

Examples of the vinyl alcohol resin include anion-modified vinyl alcohol resins such as carboxyl group-modified vinyl alcohol resins, sulfonic acid group-modified vinyl alcohol resins, and phosphate group-modified vinyl alcohol resins, cation-modified vinyl alcohol resins, and modified vinyl alcohol resins copolymerized with ethylene, vinyl ethers having long-chain alkyl groups, vinyl esters, (meth)acrylamide, alpha olefins, etc.

The degree of polymerization of the vinyl alcohol resin is not particularly limited, but may be, for example, 100 to 5,000, and preferably 500 to 3,000.

The isobutylene resin may be a homopolymer of isobutylene, or an isobutylene copolymer, which is a copolymer of isobutylene and another monomer. In the isobutylene copolymer, the other monomer that is copolymerized with isobutylene is not particularly limited. For example, a monomer having an ethylenic double bond may be mentioned.

Examples of monomers having an ethylenic double bond include ethylenically unsaturated carboxylic acids such as maleic acid (anhydride), acrylic acid, methacrylic acid, phthalic acid (anhydride), and itaconic acid (anhydride). Chemically modified isobutylene copolymers may also be used.

The molecular weight of the isobutylene copolymer is not particularly limited, but may be, for example, 3×10 ³ to 2×10 ⁵ , and preferably 5×10 ³ to 1.7×10 ⁵ , and the like.

Examples of the polyamide resin include water-soluble nylons that are chemically modified nylons such as polycaproamide (nylon-6).

The polyester resin may be, for example, a water-soluble polyester in which a component having a hydrophilic group is introduced as a copolymer component into the polyester.

Examples of thermosetting resins include melamine-based resins.

Examples of the melamine-based resin include melamine resin obtained by polymerization reaction between melamine and aldehyde, and copolymer resin of a monomer or its prepolymer used to form melamine resin and another monomer or its prepolymer. In the melamine resin, the aldehyde polymerized with melamine is not particularly limited. For example, melamine resin obtained by polymerization reaction between melamine and formaldehyde can be mentioned.

Examples of the polysaccharides include cellulose derivatives such as hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, and carboxymethyl cellulose, and natural polymeric compounds such as gum arabic, xanthan gum, curdlan, starch, dextrin, glucomannan, agarose, carrageenan, guar gum, locust bean gum, tragacanth gum, quince seed gum, pullulan, agar, and konjac mannan.

Other water-soluble adhesive components include, for example, water-soluble adhesive components mainly composed of polyethylene glycol, partially neutralized sodium polyacrylate, polyvinylpyrrolidone, copolymers of polyvinylpyrrolidone, sodium polyacrylate, copolymers of sodium polyacrylate, sodium alginate, sucrose, dextrose, fructose, lactose, gelatin, etc. These may be used alone or in combination of two or more.

When the water-soluble adhesive component is particulate, the average particle size is not particularly limited, but the average particle size of the water-soluble adhesive component is usually 0.1 μm or more, and preferably 1 μm or more. The upper limit of the average particle size of the water-soluble adhesive component is usually 250 μm or less, and preferably 200 μm or less.

The content of the adhesive component in the powder for layered manufacturing is not particularly limited. The content of the adhesive component can be, for example, 1 part by mass or more, 2 parts by mass or more, 3 parts by mass or more, 5 parts by mass or more, 8 parts by mass or more, and, for example, 40 parts by mass or less, 20 parts by mass or less, 10 parts by mass or less, per 100 parts by mass of the total amount of the powder for layered manufacturing.

Among the above water-soluble adhesive components, the polyvinyl alcohol resin is preferably a partially or completely saponified product of polyvinyl acetate, and the degree of saponification is preferably 85 to 90 mol %, since this provides higher early strength development.

In addition, in the above-mentioned modeling powder, the mass ratio of polyvinyl alcohol resin to the above-mentioned base material particles is preferably, for example, 0.005 to 0.20. If the above ratio is within the above range, the de-powdering property is high. The above ratio is preferably 0.01 to 0.15, and more preferably 0.015 to 0.10.

In addition, the average particle size (median diameter, D50) of the polyvinyl alcohol resin is preferably 10 to 150 μm, more preferably 30 to 90 μm, in order to obtain high bending strength. In addition, if the polyvinyl alcohol resin is mixed and ground with an inorganic binder to adjust the particle size, it can be made finer and mixed homogeneously, and the early strength development of the hydraulic composition is further improved.

Furthermore, the polyvinyl alcohol resin may be used, for example, in a powder form, mixed with the oxide and sand described below, or dissolved in water described below.

Furthermore, the above-mentioned shaped object preferably contains, for example, 50 parts by mass or more of the oxide relative to 100 parts by mass of the entire shaped object, and may be 60 parts by mass or more, 70 parts by mass or more, 80 parts by mass or more, 85 parts by mass or more, or 90 parts by mass or more.

In addition, in the above-mentioned modeling powder, known additives that can be used in powders for three-dimensional modeling, such as inorganic powders other than the above-mentioned oxides, dispersants, thickeners, printing aids, etc., can be used within a range that does not impair the effects of the present invention.

The inorganic powder other than the oxide is, for example, a nitride, a carbide, a sulfide, etc., and examples thereof include one or more types selected from SiC, Si ₃ N ₄ , AlN, etc.

The shape of the inorganic powder other than the oxide may be, for example, spherical, elliptical, non-spherical, etc. The average particle size (median diameter, D50) of the inorganic powder is not particularly limited, but may be, for example, 1 μm or more and 200 μm or less. From the viewpoint of moldability, the average particle size of the inorganic powder may be, for example, 5 μm or more, 10 μm or more, 20 μm or more, 30 μm or more, or 40 μm or more. The average particle size of the inorganic powder may be, for example, 200 μm or less, and may be 140 μm, 120 μm, 100 μm, 80 μm, or 60 μm or less.

The method for preparing the powder for molding is not particularly limited. For example, the components contained in the powder for molding can be mixed using a well-known mixing method such as premixing. The manner in which the components are mixed is not particularly limited. For example, all the components may be mixed at once, or they may be mixed in an appropriately set order.

The above modeling powder is typically mixed with a modeling liquid containing water and used to model objects.

The solvent used in the modeling liquid is preferably a solvent containing water. Examples of the solvent include pure water, ultrapure water, ion-exchanged water (deionized water), and distilled water. The modeling liquid may further contain an organic solvent that can be mixed uniformly with water, such as a lower alcohol or a lower ketone, as necessary. Usually, it is preferable that 40% or more of the solvent contained in the modeling liquid is water, and more preferably 50% or more, typically 50 to 100% by volume is water. Such a modeling liquid can be mixed at a ratio of, for example, 20 to 80 parts by weight, typically 40 to 60 parts by weight, per 100 parts by weight of the powder for three-dimensional modeling during modeling.

The modeling liquid may further contain, as necessary, known additives that can be used in modeling liquids, such as dyes, organic pigments, inorganic pigments, wetting agents, and flow rate enhancers, within the scope of the present invention. The content of the additives may be appropriately set depending on the purpose of their addition.

The method of forming a model using the modeling powder is not particularly limited. For example, a model can be formed by forming a layer of powder using the modeling powder and then supplying a modeling liquid containing water to a predetermined area of the layer. This modeling can be performed, for example, using a 3D printer that forms a solid object based on three-dimensional data corresponding to the model to be formed. The 3D printer can have, for example, an inkjet that drips modeling liquid containing water, and a table on which the modeling powder is placed.

In the above-mentioned molding method, for example, the following steps 1 to 3 are repeated to sequentially stack layered solids to form a shaped object.
Operation 1: The above-mentioned molding powder is layered on a mounting table so as to have a thickness corresponding to each layer of the object to be molded, for example, 0.01 mm to 0.5 mm.
Operation 2: A modeling liquid containing water is dropped from an inkjet head onto the part of the layered modeling powder (deposit) that should be cured. The water-soluble adhesive component contained in the dropped part is dissolved to bond the base material particles together, forming a layered solid.
Operation 3: The table is lowered vertically downward by an amount corresponding to the thickness of each layer of the layered solid material.

After the above operations, the unhardened modeling powder is finally removed to complete the modeling of the object. The model is formed by adhering a large number of base material particles with the dissolved water-soluble adhesive component, and may have a porous structure. After modeling, the obtained model may be naturally dried. There is no particular limit to the drying time, but it is, for example, about 1.5 hours to 24 hours, and preferably 15 hours to 20 hours.

Additive manufacturing equipment for producing the above-mentioned shaped body is not particularly limited, but examples include binder injection type powder lamination molding equipment such as ProJet 660 Pro manufactured by 3D Systems, S-Max manufactured by ExOne, VX4000 manufactured by Voxeljet, and SCM-1800 manufactured by Seemet.

<Method for improving the strength of a molded object>
The method for improving strength of a shaped object of the present invention comprises the steps of:
A step (1) of impregnating a shaped object containing an oxide containing at least one element selected from the group consisting of Si, Al, Ca, Zr, Ti, Fe, Cr, and Mg with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution;
A step (2) of subjecting the shaped object treated in the step (1) to a heat treatment at 800° C. or higher;
A step (3) of impregnating the shaped object treated in the step (2) with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution; and
The method includes a step (4) of subjecting the shaped object treated in the step (3) to a heat treatment at 800° C. or higher,
At least one of the above step (2) or the above step (4) is a heat treatment at 1000° C. or higher.

The above-mentioned step (1) is a step of impregnating the above-mentioned shaped object with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution (hereinafter, also referred to as "impregnation step (1)").

The silica-containing liquid is at least one selected from a silica sol solution, which is a colloidal solution in which ultrafine particles of silicic anhydride at the nano level are dispersed, and a non-monomer alkyl silicate solution. Of these, the dispersion medium of the silica sol solution is water or a water-soluble organic solvent, and the dispersion medium of the alkyl silicate solution is a water-soluble organic solvent. Among the dispersion solvents, organic solvents are preferred because they do not react with the above-mentioned molded object and cause little dimensional change in the molded object.

The alkyl group of the alkyl silicate is easily available, and examples thereof include a methyl group, an ethyl group, and an isopropyl group. These may be used alone or in combination of two or more.

The alkyl silicate in the alkyl silicate solution is preferably a dimer or higher alkyl silicate. Monomeric alkyl silicate is excluded from the alkyl silicate solution because the bending strength of a molded object impregnated with a monomeric alkyl silicate solution is low and the surface can be scratched with fingers. Furthermore, from the viewpoint of increasing the strength of the molded object, the alkyl silicate in the alkyl silicate solution is preferably a pentamer or higher alkyl silicate.

The viscosity of the silica-containing liquid at 25°C is preferably 50 mPa·s or less, more preferably 40 mPa·s, and even more preferably 30 mPa·s, in order to enhance the penetration into the molded object.

The impregnation step (1) is not particularly limited, but may be, for example, spraying or applying a silica-containing liquid to the molded object, or immersing the molded object in the silica-containing liquid. The penetration depth of the silica-containing liquid is preferably 0.4 to 10.0 mm. If the penetration depth is less than 0.4 mm, the bending strength of the molded object is low and the surface condition is poor, and if it exceeds 10.0 mm, it takes a long time for penetration, resulting in a decrease in manufacturing efficiency. The penetration depth of the silica-containing liquid is more preferably 0.5 to 6 mm. The penetration depth was determined by cutting the molded object after the impregnation treatment (and further after the heat treatment) with a diamond cutter and measuring the silica impregnated area on the cross section. The impregnated area was determined with the naked eye, a microscope, an optical microscope, and a scanning electron microscope.

The permeation time of the silica-containing liquid is preferably 5 to 120 seconds. If the permeation time is less than 5 seconds, the permeation is insufficient, and if it exceeds 120 seconds, the permeation tends to become saturated. The immersion time of the silica-containing liquid is more preferably 10 to 100 seconds. In addition, it is recommended that the molded product after permeation with the silica-containing solution be left to stand for 6 hours to 2 days to promote the diffusion of the silica-containing solution in the molded product.

The above step (2) is a step of subjecting the molded object processed in the above step (1) to a heat treatment at 800°C or higher (hereinafter also referred to as "heating step (2)").

The heating step (2) is not particularly limited as it depends on the size of the object, but examples include a heating method in which the object is heated to 800-2000°C in an electric furnace over 2-10 hours, held at the temperature for 30 minutes to 2 hours, and then cooled to room temperature over a further 2-10 hours. When the object is heated to 500°C or higher, most of the bound water of the minerals and polyvinyl alcohol resulting from the hydration reaction of the cement volatilizes, and the volatile content decreases the higher the temperature is heated. On the other hand, the object may melt if heated to a temperature above 2000°C. The heating temperature of the object may be 850-1800°C, 900-1600°C, 950-1400°C, or 1000-1200°C.

The heating step (2) is generally performed using an electric furnace or a combustion furnace, but is not limited to these. For example, in casting, the object heats up when it comes into contact with the molten metal.

The above step (3) is a step of impregnating the shaped object treated in the above step (2) with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution (hereinafter, also referred to as "impregnation step (3)").

The above impregnation step (3) can be carried out in the same manner as impregnation step (1) as appropriate.

The above step (4) is a step of subjecting the molded object processed in the above step (3) to a heat treatment at 800°C or higher (hereinafter also referred to as "heating step (4)").

The heating step (4) can be carried out in the same manner as the heating step (2) as appropriate.

However, at least one of the above steps (2) or (4) is a heat treatment at 1000°C or higher. By having the above configuration, for example, the bending strength can be made 10 MPa or higher.

In addition to the above steps (1) to (4), the method may further include a step of impregnating the shaped object treated in step (4) with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution (hereinafter also referred to as "impregnation step (5) etc."), and a step of heating the shaped object treated in step (5) at 800°C or higher (hereinafter also referred to as "heating step (6) etc."). (Furthermore, impregnation step (7) and heating step (8), impregnation step (9) and heating step (10), impregnation step (11) and heating step (12), etc.) The impregnation step (5) etc. and heating step (6) etc. may be appropriately performed in the same manner as the above steps (1) to (4).

In addition to the above steps (1) to (4) (including the impregnation step (5) and the heating step (6)), steps such as a heating step at less than 800°C and a drying step can be included before and after each step.

<Method of manufacturing reinforced object>
The method for producing a reinforced shaped object of the present invention comprises the steps of:
A step (1) of impregnating a shaped object containing an oxide containing at least one element selected from the group consisting of Si, Al, Ca, Zr, Ti, Fe, Cr, and Mg with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution;
A step (2) of subjecting the shaped object treated in the step (1) to a heat treatment at 800° C. or higher;
A step (3) of impregnating the shaped object treated in the step (2) with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution; and
The method includes a step (4) of subjecting the shaped object treated in the step (3) to a heat treatment at 800° C. or higher,
At least one of the above step (2) or the above step (4) is a heat treatment at 1000° C. or higher.

In the manufacturing method of the present invention, a reinforced object is an object whose strength has been improved by a method including the above steps (1) to (4).

The above steps (1) to (4) can be carried out appropriately in the same manner as the above steps (1) to (4) in the above-mentioned strength improvement method (which may further include an impregnation step (5) and a heating step (6), etc.).

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[Examples 1 to 7, Comparative Examples 1 to 10]
A binder injection type powder lamination molding machine (product name: ProJet160Pro, manufactured by 3D Systems) was used as an additive manufacturing device to mold a test body (molded body) with a cross-sectional dimension of 16 mm in length, 10 mm in width, and 80 mm in length. After performing each treatment, the test body was used for each measurement and evaluation. The materials used are shown in Table 1. The water amount setting value from the nozzle of the device was 88% in the inside (core) of the molded body and 122% in the outside (shell).

(Powder A)
As the powder A in Table 1 above, a hydraulic composition for additive manufacturing devices was used, which was obtained by mixing the following (1) calcium aluminate, (2) Espearl, (3) Cerabeads, and (4) ground Cerabeads in a weight ratio of 0.3:1:1:0.7 to obtain 100 mass% mixture, and adding 2 mass% of (5) polyvinyl alcohol.

(1) Calcium aluminate As a sample of amorphous calcium aluminate, one having a CaO/Al ₂ O ₃ molar ratio of 2.2, a vitrification rate of 95% or more, and a Blaine specific surface area of 2710 cm ² /g was used. D50 was 24 μm.

(2) Espearl Espearl #180L (manufactured by Yamakawa Sangyo Co., Ltd., alumina-based spherical low-expansion aggregate) was used. The chemical composition is shown in the table below. D50 was 75 μm.

(3) Cerabeads Naigai Cerabeads #1450 (manufactured by Itochu Ceratec Co., Ltd., artificial ceramic sand made of mullite crystals) was used. The chemical composition is shown in the table below.

(4) Crushed Cerabeads The above-mentioned NAIGAI Cerabeads were crushed in a ball mill to produce a powder having a D50 of 30 μm.

(5) Polyvinyl alcohol Part number 22-88 S1 (PVA217SS, manufactured by Kuraray Co., Ltd.) was used. The degree of saponification was 87 to 89%, the average particle size (D50) was 60 μm, the content of particles larger than 94 μm was 29%, and the content of particles larger than 77 μm was 47% by mass, the 10% diameter (D10) was 25 μm, and the 90% diameter (D90) was 121 μm.

(Silica Liquid B)
Silica sol dispersed in isopropyl alcohol (IPA-ST, manufactured by Nissan Chemical Industries, Ltd.) was used as the silica liquid B in Table 1. The chemical composition and the like are shown below.
・Solid content wt%: 30wt%
・Particle size: 10-15nm
Viscosity at 25°C: 1.0 to 20.0 mPa·s
- Moisture content: 2% or less

The obtained molded bodies were subjected to tests under the various conditions shown in Table 4.

<Processing conditions in Examples and Comparative Examples>
Example 1: Impregnation treatment → Heat treatment at 1100°C → Impregnation treatment → Heat treatment at 100°C → Impregnation treatment → Heat treatment at 100°C → Impregnation treatment → Heat treatment at 1100°C
Example 2: Impregnation treatment → Heat treatment at 1100°C → Impregnation treatment → Heat treatment at 1100°C
Example 3: Impregnation treatment → Heat treatment 1100°C → Impregnation treatment → Heat treatment 1100°C → Impregnation treatment → Heat treatment 1100°C
Example 4: Impregnation treatment → Heat treatment 1100°C → Impregnation treatment → Heat treatment 1100°C → Impregnation treatment → Heat treatment 1100°C → Impregnation treatment → Heat treatment 1100°C
Example 5: Impregnation treatment → Heat treatment 1100°C → Impregnation treatment → Heat treatment 1100°C → Impregnation treatment → Heat treatment 1100°C → Impregnation treatment → Heat treatment 1100°C → Impregnation treatment → Heat treatment 1100°C
Example 6: Impregnation treatment → Heat treatment at 800°C → Impregnation treatment → Heat treatment at 1100°C
Example 7: Impregnation treatment → Heat treatment at 1100°C → Impregnation treatment → Heat treatment at 800°C
Comparative Example 1: Impregnation treatment → Heat treatment 100°C
Comparative Example 2: Impregnation treatment → Heat treatment at 100°C → Impregnation treatment → Heat treatment at 100°C → Impregnation treatment → Heat treatment at 100°C
Comparative Example 3: Impregnation treatment → Heat treatment at 100°C → Impregnation treatment → Heat treatment at 100°C → Impregnation treatment → Heat treatment at 1100°C
Comparative Example 4: Impregnation treatment → Heat treatment 1100°C
Comparative Example 5: Impregnation treatment → Heat treatment at 1100°C → Impregnation treatment → Heat treatment at 100°C
Comparative Example 6: Impregnation treatment → Heat treatment at 1100°C → Impregnation treatment → Heat treatment at 100°C → Impregnation treatment → Heat treatment at 100°C
Comparative Example 7: Impregnation treatment → Heat treatment at 1100°C → Impregnation treatment → Heat treatment at 100°C → Impregnation treatment → Heat treatment at 100°C → Impregnation treatment → Heat treatment at 100°C
Comparative Example 8: Impregnation treatment → Heat treatment at 800°C
Comparative Example 9: Impregnation treatment → Heat treatment 1500°C
Comparative Example 10: Untreated molded body

*Details of each treatment For the impregnation treatment, the molded body was placed in a container filled with silica-containing liquid so that the entire body was immersed, and after leaving it to stand for 60 seconds, it was removed from the silica-containing liquid and dried for 24 hours. For example, in the case of a 100°C heat treatment, the molded body was placed in a dryer (Tokyo Rika Kikai Co., Ltd., model number: LTI-600SD) set to 100°C and left to stand for 24 hours, after which the dryer was turned off and it was slowly cooled to room temperature. In the case of heating to a heating temperature of 800°C or higher, a trolley-lifting high-temperature atmospheric furnace (Nemus Co., Ltd., model number: WUD70x70x70-2Z2-12) was used to gradually increase the temperature to the top temperature, and after holding at each top temperature for 1 hour, it was slowly cooled to room temperature. The heating and cooling rates were both set to 200°C/1h.
Impregnation treatment: Impregnation treatment in silica liquid B for 60 seconds Heat treatment at 100°C: Heat treatment at 100°C for 24 hours Heat treatment at 800°C: Heat treatment at 800°C for 1 hour Heat treatment at 1100°C: Heat treatment at 1100°C for 1 hour Heat treatment at 1500°C: Heat treatment at 1500°C for 1 hour

The bending strength results are shown in Table 5 and Figures 1 to 3. Table 5 also shows the results of dimensional change and mass loss.

<Measurement and evaluation conditions>
(Bending strength measurement, dimensional change measurement)
Using the molded articles that had undergone each treatment, a three-point bending test was carried out using a bending strength tester (model number: MODEL-2257, manufactured by Aiko Engineering Co., Ltd.) to measure the bending strength and dimensions of each of the treated molded articles.

(Measurement of mass reduction rate)
The mass loss rate of each treated molded body was measured using a thermal analyzer (manufactured by Bruker A.X., model number: TG-DTA2000SR). The temperature was raised from room temperature to 1000°C at 20°C/min, and the mass loss rate was calculated from the change in mass of the sample at room temperature and 1000°C.

<Criteria>
In the measurements of bending strength, dimensional change, and mass reduction rate, the desired reinforced objects were those that satisfied the following criteria.
・Bending strength standard: 10 MPa or more ・Dimensional standard: ±2% or less ・Mass reduction rate standard: 0.5 or less (related to the amount of gas generated; if too much gas is generated, defects will occur in the casting, etc.)

As shown in Table 5 and Figures 1 to 3, the results of each evaluation showed that the moldings of Examples 1 to 7 all showed the desirable strength improvement effects described above in bending strength measurements, dimensional change measurements, and mass reduction rate measurements.

Claims (13)

A step (1) of impregnating a shaped object containing an oxide containing Ca with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution;
A step (2) of subjecting the shaped object treated in the step (1) to a heat treatment at 800° C. or higher;
A step (3) of impregnating the shaped object treated in the step (2) with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution; and
A step (4) of subjecting the shaped object treated in the step (3) to a heat treatment at 800° C. or higher,
At least one of the steps (2) and (4) is a heat treatment at 1000° C. or higher;
The method for improving strength of a shaped object, wherein the alkyl silicate in the alkyl silicate solution is an alkyl silicate having a dimer or higher . The method for improving the strength of a molded object according to claim 1, wherein the molded object is manufactured by an additive manufacturing device. The strength improvement method according to claim 1 or 2, wherein the shaped object contains 50 mass% or more of the oxide relative to the entire shaped object. The strength improvement method according to any one of claims 1 to 3, wherein the impregnation treatment in step (1) is carried out for 5 to 120 seconds. The strength improvement method according to any one of claims 1 to 4, wherein the alkyl silicate in the alkyl silicate solution is an alkyl silicate having a pentamer or more. The strength improving method according to any one of claims 1 to 5 , wherein the shaped object further contains at least one element selected from the group consisting of Si, Al, Zr, Ti, Fe, Cr, and Mg . The strength improvement method according to any one of claims 1 to 6, wherein the heat treatment in step (2) is at 2000°C or less. The strength improvement method according to any one of claims 1 to 7, wherein the heat treatment in step (4) is at 2000°C or less. moreover,
A step (5) of impregnating the shaped object treated in the step (4) with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution; and
The strength improving method according to any one of claims 1 to 8, further comprising a step (6) of subjecting the shaped object treated in the step (5) to a heat treatment at 800°C or higher. The strength improvement method according to claim 9, wherein the heat treatment in step (6) is performed at 2000°C or less. The strength improvement method according to any one of claims 1 to 10, wherein the shaped object is used for a casting mold. A step (1) of impregnating a shaped object containing an oxide containing Ca with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution;
A step (2) of subjecting the shaped object treated in the step (1) to a heat treatment at 800° C. or higher;
A step (3) of impregnating the shaped object treated in the step (2) with at least one type of silica sol solution or a silica-containing liquid containing an alkyl silicate solution; and
A step (4) of subjecting the shaped object treated in the step (3) to a heat treatment at 800° C. or higher,
At least one of the steps (2) and (4) is a heat treatment at 1000° C. or higher;
A method for producing a reinforced shaped article, wherein the alkyl silicate in the alkyl silicate solution is an alkyl silicate having a dimer or higher . The method for producing a reinforced shaped article according to claim 12 , wherein the shaped article further contains at least one element selected from the group consisting of Si, Al, Zr, Ti, Fe, Cr, and Mg .