JP7738325B2 - Light-curing water-based slurry - Google Patents

Description

The present invention relates to a photocurable aqueous slurry.

In recent years, there has been a great deal of interest in three-dimensional printing technology for ceramic materials, due to the expectation that it will be possible to manufacture components with complex shapes designed using CAD and other tools with high precision and high productivity.

In particular, stereolithography excels at producing high-resolution images, and is expected to lead to the creation of next-generation materials that are difficult to design using conventional manufacturing processes, such as tailor-made biomaterials such as artificial bones and teeth, reactor materials with unique material transport pathways, and microstructural components for small precision instruments.

Ceramic materials that utilize 3D stereolithography are generally formed into complex shapes by selectively irradiating light onto a slurry in which fine ceramic raw material particles are highly dispersed in a photocurable monomer. Another method is to pour the slurry into a 3D molded resin mold and allow it to solidify.

The hardened body obtained in this way is densified through a firing process, but because the typical slurries mentioned above contain a large amount of resin, firing operations must be carried out over a long period of time with extremely slow temperature rise conditions to prevent cracking or collapse of the molded object. In other words, designing a stimulus-responsive slurry with a low resin content is essential to improving the productivity of ceramic materials that undergo stereolithography processes.

In response to these issues, Patent Document 1 discloses a photocurable slurry for three-dimensional optical shaping that is distinct from conventional curing principles, as it is capable of photocrosslinking inorganic particles suspended in a solvent with only a small amount of monomer. It also discloses that the photocurable slurry described in Patent Document 1 achieves excellent dispersion stability of inorganic particles in a slurry containing a high concentration of inorganic particles.

Japanese Patent Application Laid-Open No. 2019-70064

However, the photocurable slurry described in Patent Document 1 uses a large amount of organic solvent, posing a safety issue for the working environment.

In order to solve these problems, the present invention aims to provide a photocurable aqueous slurry that is capable of photocrosslinking inorganic particles in a slurry with a very small amount of monomer, has excellent dispersion stability of inorganic particles in the slurry, and is safe for the working environment.

The above problems are solved by the present invention, which is specified as follows.
1. A photocurable aqueous slurry containing (1) inorganic particles, (2) a polyalkyleneimine or a modified polyethyleneimine having a structure in which a compound having a polyethylene glycol chain is added to polyethyleneimine, (3) a water-soluble acrylate, and (4) a photopolymerization initiator.
2. The photocurable aqueous slurry according to 1 above, wherein the content of the water-soluble acrylate is 1.5% by mass to 10.0% by mass relative to the inorganic particles.
3. The photocurable aqueous slurry according to 1 or 2 above, wherein the polyalkyleneimine and the modified polyethyleneimine each have a weight average molecular weight of 300 to 50,000.
4. The photocurable aqueous slurry according to any one of 1 to 3 above, wherein the content of the inorganic particles is 10% by volume to 65% by volume.
5. (5) The photocurable aqueous slurry according to any one of 1 to 4 above, further comprising a dispersant which is an anionic polymer.

According to the present invention, it is possible to photocrosslink inorganic particles in a slurry with only a small amount of monomer, thereby providing a photocurable aqueous slurry that has excellent dispersion stability of inorganic particles in the slurry and is safe for the working environment.

1 is a graph showing the relationship between shear rate and apparent viscosity for a photocurable aqueous slurry prepared using 4-HBA as the water-soluble acrylate and an ultraviolet light polymerization initiator as the polymerization initiator. 1 is a graph showing the relationship between shear rate and apparent viscosity for a photocurable aqueous slurry prepared using 4-HBA as the water-soluble acrylate and a blue light polymerization initiator as the polymerization initiator. 1 is a graph showing the relationship between shear rate and apparent viscosity for a photocurable aqueous slurry prepared using PEGDA as the water-soluble acrylate and an ultraviolet light polymerization initiator as the polymerization initiator. 1 is a graph showing the relationship between the curing time and the storage modulus for a photocurable aqueous slurry prepared using 4-HBA as the water-soluble acrylate and an ultraviolet light polymerization initiator as the polymerization initiator. 1 is a graph showing the relationship between the curing time and the storage modulus for a photocurable aqueous slurry prepared using 4-HBA as the water-soluble acrylate and a blue light polymerization initiator as the polymerization initiator. 1 is a graph showing the relationship between the curing time and the storage modulus for a photocurable aqueous slurry prepared using PEGDA as the water-soluble acrylate and an ultraviolet light polymerization initiator as the polymerization initiator.

Next, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and it should be understood that appropriate design changes and improvements may be made based on the common knowledge of those skilled in the art without departing from the spirit of the present invention.

<Photo-curable water-based slurry>
The photocurable aqueous slurry according to an embodiment of the present invention contains inorganic particles, polyalkyleneimine or modified polyethyleneimine having a structure in which a compound having a polyethylene glycol chain is added to polyethyleneimine (hereinafter, also simply referred to as "modified polyethyleneimine"), a water-soluble acrylate, and a photopolymerization initiator.

More specifically, the photocurable aqueous slurry according to an embodiment of the present invention comprises inorganic particles having polyalkyleneimine or modified polyethyleneimine, which has a structure in which a compound having a polyethylene glycol chain is attached to polyethyleneimine, attached to at least a portion of the surface thereof, dispersed in an aqueous solvent containing a water-soluble acrylate and a photopolymerization initiator.

[Inorganic particles]
In the photocurable aqueous slurry according to the embodiment of the present invention, the inorganic particles are not particularly limited as long as polyethyleneimine or modified polyethyleneimine can adhere to at least a portion of their surfaces in an aqueous solvent. Examples of the inorganic particles include particles of inorganic compounds such as silicon oxide ( _SiO2 ), _silicon nitride ( _Si3N4 ), hydroxyapatite ( _Ca10 ( _PO4 ) ₆ (OH) ₂ ), aluminum oxide ( _Al2O3 ), zirconium oxide ( _ZrO2 ), aluminum nitride (AlN), boron nitride (BN), yttrium oxide ( _Y2O3 ), zinc oxide ₍ ZnO), titanium oxide ( _TiO2 ), calcium carbonate ( _CaCO3 ), _and barium titanate ( _BaTiO3 ), as well as particles of nickel (Ni) and silicon (Si).

The specific surface area diameter of the inorganic particles is preferably 10 nm to 10 μm, and more preferably 30 nm to 5 μm. If the specific surface area diameter of the inorganic particles is 10 nm or more, polyethyleneimine or modified polyethyleneimine will adhere more easily to the surface. If the specific surface area diameter of the inorganic particles is 10 μm or less, complex-shaped components can be molded without the shape collapsing. Here, the "specific surface area diameter" of the inorganic particles in the photocurable aqueous slurry according to an embodiment of the present invention is a numerical value determined by the following method. That is, the specific surface area of the inorganic particles in the photocurable aqueous slurry according to an embodiment of the present invention is determined by gas adsorption, and the diameter geometrically calculated from the specific surface area when the particle shape is considered spherical is defined as the specific surface area diameter.

In the photocurable aqueous slurry according to an embodiment of the present invention, the content of inorganic particles is preferably 10% to 65% by volume, and more preferably 40% to 50% by volume. If the content of inorganic particles is 10% by volume or more, a decrease in mechanical strength can be suppressed even when a complex shape is imparted to an inorganic molded article in which inorganic particles are strongly cross-linked. If the content of inorganic particles is 65% by volume or less, the inorganic particles having polyalkyleneimine attached to their surfaces can be dispersed uniformly and stably in the aqueous solvent.

[Water-soluble acrylate]
In the photocurable aqueous slurry according to the embodiment of the present invention, the water-soluble acrylate preferably contains at least one of a water-soluble polyfunctional acrylate and a water-soluble monofunctional acrylate having a hydrogen-bonding site (such as a hydroxyl group, an amide group, or a polyethylene glycol chain).
Examples of the water-soluble polyfunctional acrylate include modified trimethylolpropane triacrylate, polyethylene glycol diacrylate, N,N'-{[(2-acrylamido-2-[(3-acrylamidopropoxy)methyl]propane-1,3-diyl)bis(oxy)]bis(propane-1,3-diyl)}diacrylamide, N,N',N''-triacryloyldiethylenetriamine, N,N'-diacrylloy-4,7,10-trioxa-1,13-tridecanediamine, and N,N',N'',N'''-tetraacryloyltriethylenetetraamine.
Examples of water-soluble monofunctional acrylates having a hydrogen bonding site include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, ethoxydiethylene glycol acrylate, methoxytriethylene glycol acrylate, methoxypolyethylene glycol acrylate, N,N-dimethylacrylamide, N-methoxymethylacrylamide, and N-hydroxymethylacrylamide.
The structural formula of 4-HBA (4-hydroxybutyl acrylate), a water-soluble monofunctional acrylate having a hydrogen bonding site, is shown in formula (1) below. The structural formula of PEGDA (polyethylene glycol diacrylate), a water-soluble multifunctional acrylate, is shown in formula (2) below.

In the photocurable aqueous slurry according to an embodiment of the present invention, the content of the water-soluble acrylate is preferably 1.5% to 10.0% by mass relative to the inorganic particles, and more preferably 1.5% to 5.0% by mass. When the content of the water-soluble acrylate is 1.5% by mass or more relative to the inorganic particles, the photocurable aqueous slurry solidifies, allowing complex shapes to be formed without collapse of the molded body. When the content of the water-soluble acrylate is 10.0% by mass or less relative to the inorganic particles, cracking during the degreasing process can be effectively suppressed.

[Photopolymerization initiator]
In the photocurable aqueous slurry according to the embodiment of the present invention, the photopolymerization initiator is not particularly limited as long as it generates radicals for initiating radical polymerization of the water-soluble acrylate upon irradiating the photocurable aqueous slurry with light and is water-soluble. Examples of the photopolymerization initiator include benzyl dimethyl ketal, benzophenone, methyl 2-benzoylbenzoate, 4,4'-bis(diethylamino)benzophenone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2,2'-azobis[2-methyl-n-(2-hydroxyethyl)propionamide], and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone.

In the photocurable aqueous slurry according to an embodiment of the present invention, the content of the photopolymerization initiator is preferably 0.5% to 8.0% by mass relative to the water-soluble acrylate, and more preferably 1.0% to 5.0% by mass. When the content of the photopolymerization initiator is 0.5% by mass or more relative to the water-soluble acrylate, the photocurable aqueous slurry can be solidified in a short time, allowing complex shapes to be formed. When the content of the photopolymerization initiator is 8.0% by mass or less relative to the water-soluble acrylate, a decrease in the solidification rate of the photocurable aqueous slurry when forming complex shapes can be suppressed.

[Aqueous solvent]
The photocurable aqueous slurry according to the embodiment of the present invention contains an aqueous solvent. The photocurable aqueous slurry according to the embodiment of the present invention uses an aqueous solvent as a solvent for the inorganic particles, polyalkyleneimine or modified polyethyleneimine, water-soluble acrylate, and photopolymerization initiator, thereby improving the safety of the working environment.

The aqueous solvent used in embodiments of the present invention may be water, or a mixture of water and another aqueous solvent such as an alcohol. Examples of such alcohols include methanol, ethanol, isopropyl alcohol, isobutyl alcohol, higher alcohols, and benzyl alcohol.

In the photocurable aqueous slurry according to an embodiment of the present invention, the content of the aqueous solvent is preferably 35% to 90% by volume, and more preferably 50% to 60% by volume. If the content of the aqueous solvent is 35% by volume or more, the inorganic particles can be uniformly dispersed in the photocurable aqueous slurry. On the other hand, if the content of the aqueous solvent is 90% by volume or less, complex shapes can be molded without causing collapse of the molded body.

The photocurable aqueous slurry according to an embodiment of the present invention may contain a polymerization inhibitor to inhibit the polymerization of the water-soluble acrylate. The polymerization inhibitor is not particularly limited, and a general radical polymerization inhibitor is used depending on the type of water-soluble acrylate. The content of the polymerization inhibitor in the photocurable aqueous slurry according to an embodiment of the present invention is not particularly limited, and is adjusted appropriately depending on the type of water-soluble acrylate, the content in the photocurable aqueous slurry, etc.

[Polyalkyleneimine]
Examples of polyalkyleneimines according to the present invention include polyethyleneimine, polypropyleneimine, polybutadieneimine, etc. Among these, polyethyleneimine is more preferred because it has a high affinity with inorganic particles and improves the dispersion stability of the inorganic particles in the slurry and the long-term stability of the photocurable aqueous slurry.

The weight-average molecular weight (Mw) of the polyalkyleneimine is preferably 300 to 50,000, more preferably 300 to 30,000, and even more preferably 600 to 10,000. If the weight-average molecular weight (Mw) of the polyalkyleneimine is 300 or more, the long-term stability of the photocurable aqueous slurry is improved. If the weight-average molecular weight (Mw) of the polyalkyleneimine is 50,000 or less, inorganic particles with polyalkyleneimine attached to their surfaces can be dispersed uniformly and stably in the aqueous solvent in the photocurable aqueous slurry. The weight-average molecular weight can be confirmed by GPC-MALS.

[Modified polyethyleneimine]
The modified polyethyleneimine (PEI-mPEG) according to an embodiment of the present invention has a structure in which a compound having a polyethylene glycol chain is added to polyethyleneimine (PEI), as exemplified by the following formula (3). Note that the structure of the modified polyethyleneimine is not limited to that of the following formula (3).

(In equation (3), n≒4.)

As shown in formula (3), modified polyethyleneimine has a structure in which a compound having a polyethylene glycol chain (hereinafter sometimes referred to as a " _PEG chain") is added to the nitrogen atom of some ethyleneimine structural units ( _-CH2CH2NH- ) present in a polyethyleneimine (PEI) molecule. This modified polyethyleneimine (PEI-mPEG) can be synthesized by reacting polyethyleneimine with modified polyethylene glycol, in which the terminal of the polyethylene glycol has been modified with a functional group such as acrylate that reacts with amines. The modified polyethyleneimine (PEI-mPEG) exemplified in formula (3) has a structure in which polyethylene glycol monomethyl ether acrylate is used as the compound having a PEG chain and this is subjected to Michael addition. Such modified polyethyleneimine has a high affinity for inorganic particles, improving the dispersion stability of the inorganic particles in the slurry and the long-term stability of the photocurable aqueous slurry.

In modified polyethyleneimine (PEI-mPEG), the ratio (mol %) of the number of moles of ethyleneimine structural units to which a compound having a PEG chain has been added to the number of moles of _{ethyleneimine} structural units ( _-CH2CH2NH- ) is referred to as the "PEG addition ratio" in this specification. The PEG addition ratio is expressed by the following formula (A):
PEG addition rate (mol%)=100×MPEG/MEI (A)

In the above formula (A), MEI is the number of moles of ethyleneimine structural units, and MPEG is the number of moles of ethyleneimine structural units to which a compound having a polyethylene glycol chain (PEG chain) has been added. MEI can be calculated by dividing the mass (g) of polyethyleneimine (PEI) used in synthesizing the modified polyethyleneimine (PEI-mPEG) by the formula weight of the ethyleneimine structural unit, 43.1 (g/mol). MPEG can be calculated by dividing the mass of the compound having a PEG chain in the modified polyethyleneimine (PEI-mPEG) by the weight-average molecular weight of the compound having a PEG chain. When the synthesized modified polyethyleneimine (PEI-mPEG) is measured by ^1H -NMR (nuclear magnetic resonance), if no peak corresponding to a functional group (e.g., an acryloyl group) of the compound having a PEG chain (e.g., polyethylene glycol monomethyl ether acrylate) used in the addition reaction is detected, this indicates that the entire amount of the compound having a PEG chain introduced into the reaction vessel was consumed in the addition reaction. In this case, the number of moles of the compound having an attached PEG chain can be considered to be equal to the number of moles of the compound having a PEG chain introduced into the reaction vessel.

The weight-average molecular weight (Mw) of the modified polyethyleneimine is preferably 300 to 50,000, more preferably 500 to 50,000, and even more preferably 1,000 to 30,000. If the weight-average molecular weight (Mw) of the modified polyethyleneimine is 300 or more, the long-term stability of the photocurable aqueous slurry is further improved. If the weight-average molecular weight (Mw) of the modified polyethyleneimine is 50,000 or less, inorganic particles with modified polyethyleneimine attached to their surfaces can be dispersed uniformly and stably in the aqueous solvent in the photocurable aqueous slurry. The weight-average molecular weight can be confirmed using the GPC-MALS method.

In the photocurable aqueous slurry according to an embodiment of the present invention, the content of polyalkyleneimine or modified polyethyleneimine is preferably 0.3 mg/ ^m to 3.0 mg/m, and more preferably 0.8 mg/ ^m to 2.0 mg/ ^m , based on the surface ^area of the inorganic particles. When the content of polyalkyleneimine or modified polyethyleneimine is 0.3 mg/m or ^more , it can be adhered to almost the entire surface of the inorganic particles. When the content of polyalkyleneimine or modified polyethyleneimine is 3.0 mg/m or ^less , in the photocurable aqueous slurry, the inorganic particles having polyalkyleneimine or modified polyethyleneimine adhered to their surfaces can be dispersed more uniformly and stably in the aqueous solvent.

[Dispersant]
The photocurable aqueous slurry according to the embodiment of the present invention may further contain a dispersant that is an anionic polymer. With this configuration, even for positively charged inorganic particles to which the positively charged polyalkyleneimine or modified polyethyleneimine cannot be sufficiently immobilized in an aqueous solution, the polyalkyleneimine or modified polyethyleneimine can be adsorbed onto the inorganic particles via the negatively charged anionic polymer.

Examples of anionic polymers that make up the dispersant include polystyrene sulfonic acid and its salts, polyacrylic acid and its salts, and acrylic acid-maleic acid copolymers and their salts.

In the photocurable aqueous slurry according to an embodiment of the present invention, the content of the dispersant is preferably 0.3 mg/ ^m to 3.0 mg/m, and more preferably 0.8 mg/ ^m to 2.0 mg/ ^m , based on the surface ^area of the inorganic particles. If the content of the dispersant is 0.3 mg/ ^m or more, the dispersant adheres to almost the entire surface of the inorganic particles, and polyalkyleneimine or modified polyethyleneimine can be adhered via the dispersant. If the content of the dispersant is 3.0 mg/m or ^less , in the photocurable aqueous slurry, the inorganic particles having polyalkyleneimine or modified polyethyleneimine adhered to their surfaces via the dispersant can be dispersed uniformly and stably in the aqueous solvent.

<Reaction mechanism of photocurable aqueous slurry>
Next, the reaction mechanism (curing mechanism) of the photocurable aqueous slurry according to the embodiment of the present invention will be described.
First, the reaction mechanism (curing mechanism) of the photocurable aqueous slurry using a water-soluble polyfunctional acrylate will be described.
When the photocurable aqueous slurry of this embodiment is irradiated with light, the photopolymerization initiator first generates radicals. This initiates radical polymerization of the water-soluble acrylate, resulting in the production of a water-soluble acrylate polymer. Furthermore, because radical polymerization is an exothermic reaction, heat is generated as the radical polymerization begins. The heat (reaction heat) resulting from this radical polymerization causes a Michael addition reaction in which amino groups of the polyalkyleneimine or modified polyethyleneimine attached to the surfaces of the inorganic particles are added to the double bonds constituting the water-soluble acrylate and its polymer. That is, the photocurable aqueous slurry of this embodiment initiates radical polymerization of the water-soluble acrylate by irradiation with light, and the heat resulting from this radical polymerization causes a Michael addition reaction between the double bonds constituting the water-soluble acrylate and its polymer and the amino groups of the polyalkyleneimine or modified polyethyleneimine. Therefore, the photocurable aqueous slurry of this embodiment does not require external heat application to cause the Michael addition reaction; simply by irradiating it with light, the radical polymerization reaction and the Michael addition reaction can occur. As a result, the photocurable aqueous slurry of this embodiment can be used to form an inorganic molded article through a simple procedure.

This Michael addition reaction crosslinks inorganic particles. The bonds resulting from the Michael addition reaction are formed by the chemical reaction shown in formula (4) below.

That is, in the above formula (4), the amino group of (a) the polyalkyleneimine or modified polyethyleneimine undergoes a Michael addition reaction with the double bond constituting (b) the water-soluble acrylate to form the bond (c) or (d).

The bond formed by such a Michael addition reaction can be confirmed, for example, by measuring the infrared absorption spectrum using infrared spectroscopy (IR). A Fourier transform infrared spectrophotometer (FT-IR) is used to measure the infrared absorption spectrum.

Next, the reaction mechanism (curing mechanism) of the photocurable aqueous slurry using a water-soluble monofunctional acrylate having a hydrogen-bonding site will be described.
When the photocurable aqueous slurry of this embodiment is irradiated with light, the photopolymerization initiator first generates radicals. This then initiates radical polymerization of the water-soluble acrylate, producing a water-soluble acrylate polymer. At this time, hydrogen-bonding groups contained in the water-soluble acrylate polymer form hydrogen bonds with the polyalkyleneimine or modified polyethyleneimine attached to the surfaces of the inorganic particles.

The photocurable aqueous slurry according to the present invention exhibits excellent dispersion stability of inorganic particles in the slurry. Furthermore, when a polyfunctional acrylate is used as the water-soluble acrylate, the reaction heat generated by the radical polymerization reaction is utilized to cause a Michael addition reaction in which amino groups of the polyalkyleneimine or modified polyethyleneimine attached to the surface of the inorganic particles are added to the double bonds constituting the water-soluble acrylate and its polymer. This allows for the formation of an inorganic molded body in which the inorganic particles are strongly crosslinked by a simple operation. Furthermore, when a water-soluble monofunctional acrylate having a hydrogen-bonding moiety is used as the water-soluble acrylate, a polymer of the water-soluble acrylate is produced by radical polymerization. At this time, the hydrogen-bonding groups contained in the water-soluble acrylate polymer form hydrogen bonds with the polyalkyleneimine or modified polyethyleneimine attached to the surface of the inorganic particles, allowing for the formation of an inorganic molded body by a simple operation.
Furthermore, the polyalkyleneimine or modified polyethyleneimine attached to the surface of the inorganic particles has a high affinity for the aqueous solvent, resulting in a low slurry viscosity and high fluidity, making it easy to cast into a mold and enabling high-resolution photolithography. Furthermore, since photocuring is possible with a small amount of monomer, when producing an inorganic molded body by curing the photocurable aqueous slurry, the inorganic molded body is less likely to crack even when subjected to high-speed firing. Furthermore, since an aqueous solvent is used as the solvent, and no organic solvent is used, the working environment is safer.

<Method for producing photocurable aqueous slurry>
In a method for producing a photocurable aqueous slurry according to an embodiment of the present invention, first, a polyalkyleneimine or a modified polyethyleneimine is added to an aqueous solvent and stirred to prepare an aqueous solution containing the polyalkyleneimine or the modified polyethyleneimine.

Next, inorganic particles and a photopolymerization initiator are dispersed in an aqueous solution containing polyalkyleneimine or modified polyethyleneimine to prepare a dispersion of inorganic particles. The method for dispersing the inorganic particles and photopolymerization initiator in the aqueous solution is not particularly limited, but examples include stirring the aqueous solution containing the inorganic particles and photopolymerization initiator using a stirring blade or magnetic stirrer, and applying ultrasound to the aqueous solution containing the inorganic particles and photopolymerization initiator.

Next, a water-soluble acrylate is added to the resulting dispersion, thereby obtaining a photocurable aqueous slurry according to an embodiment of the present invention. The method for adding and dispersing the water-soluble acrylate to the dispersion is not particularly limited, but examples include stirring the dispersion containing the water-soluble acrylate using a stirring blade or magnetic stirrer, and applying ultrasound to the dispersion containing the water-soluble acrylate.

<Inorganic molded body>
The inorganic molded body is an inorganic molded body obtained by curing the photocurable aqueous slurry according to an embodiment of the present invention.
When a polyfunctional acrylate is used as the water-soluble acrylate, it has a bond formed by a Michael addition reaction of the amino group of the polyalkyleneimine or modified polyethyleneimine with the double bond constituting the water-soluble acrylate and its polymer.
More specifically, the inorganic molded body has polyalkyleneimine or modified polyethyleneimine attached to the surface of inorganic particles, and has bonds formed by a Michael addition reaction of the amino groups of the polyalkyleneimine or modified polyethyleneimine with the double bonds that constitute the water-soluble acrylate and its polymer.
In the inorganic molding, the amino groups of the polyalkyleneimine or modified polyethyleneimine attached to the surface of the inorganic particles are strongly cross-linked to the double bonds constituting the water-soluble acrylate and its polymer by Michael addition.

In addition, in inorganic molded articles made using a water-soluble monofunctional acrylate having hydrogen-bonding sites as the water-soluble acrylate, the hydrogen-bonding groups contained in the water-soluble acrylate polymer form hydrogen bonds with the polyalkyleneimine or modified polyethyleneimine attached to the surface of the inorganic particles.

Examples of inorganic molded bodies include elastically deformable molded bodies such as rubber, and plastically deformable molded bodies.
Therefore, the inorganic molded body can be molded into a complex-shaped component (molded body). Furthermore, by sintering the inorganic molded body, a sintered body can be obtained that maintains the complex shape of the inorganic molded body.

<Method of manufacturing inorganic molded body>
In the method for producing an inorganic molded body of this embodiment, the photocurable aqueous slurry is irradiated with light to cure the photocurable aqueous slurry, thereby forming an inorganic molded body from the photocurable aqueous slurry. By irradiating the photocurable aqueous slurry with light, the water-soluble acrylate initiates radical polymerization as described above.
When a polyfunctional acrylate is used as the water-soluble acrylate, the heat generated by this radical polymerization causes a Michael addition reaction in which the amino groups of the polyalkyleneimine or modified polyethyleneimine attached to the surface of the inorganic particles are added to the double bonds that constitute the water-soluble acrylate and its polymer.
When a water-soluble monofunctional acrylate having a hydrogen-bonding moiety is used as the water-soluble acrylate, a polymer of the water-soluble acrylate is produced by this radical polymerization. At this time, the hydrogen-bonding group contained in the polymer of the water-soluble acrylate forms a hydrogen bond with the polyalkyleneimine or modified polyethyleneimine attached to the surface of the inorganic particle.
As a result, the photocurable aqueous slurry solidifies or aggregates to obtain an inorganic molded body.

For example, a photocurable aqueous slurry can be placed in a light-transmitting mold corresponding to the desired shape, and then irradiated with light to solidify or aggregate the photocurable aqueous slurry, resulting in an inorganic molded product with the outer shape of the mold. Furthermore, by using a mold with a complex shape, the outer shape of the inorganic molded product can also be made complex.

Also, for example, the photocurable aqueous slurry may be ejected from a nozzle or the like so that it takes on the desired shape, and the photocurable aqueous slurry may be irradiated with light immediately after ejection to solidify or aggregate the photocurable aqueous slurry, thereby forming an inorganic molded product having the desired shape.

By degreasing and sintering the inorganic molded body obtained in this manner, a sintered body can be obtained that maintains the complex shape of the inorganic molded body.

This method for producing inorganic molded bodies produces inorganic molded bodies in which the amino groups of the polyalkyleneimine or modified polyethyleneimine attached to the surfaces of the inorganic particles undergo Michael addition to the double bonds constituting the water-soluble acrylate and its polymer, resulting in strong cross-linking between the inorganic particles. Alternatively, inorganic molded bodies can be produced in which the hydrogen-bonding groups contained in the water-soluble acrylate polymer form hydrogen bonds with the polyalkyleneimine or modified polyethyleneimine attached to the surfaces of the inorganic particles. This makes it possible to mold components (molded bodies) with complex shapes. Furthermore, by sintering the inorganic molded body produced by this method for producing inorganic molded bodies, a sintered body can be produced in which the complex shape of the inorganic molded body is maintained.

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

<Experimental Example 1>
- Preparation of PEI-added photocurable aqueous slurry -
Polyethyleneimine (PEI, weight-average molecular weight (Mw) = 1800) was added to distilled water, and _SiO2 was further dispersed as inorganic particles. The mixture was then subjected to planetary mixing (5 minutes) and stirring using a ball mill (24 hours) to prepare a dispersion of inorganic particles.
Polyethyleneimine was added so that the content in the photocurable aqueous slurry to be prepared was 0.4 mg/m ² relative to SiO ₂ .
_SiO2 has an average particle size of about 220 nm, and was added so that its content in the photocurable aqueous slurry to be prepared was 46% by volume.
Next, a water-soluble acrylate and a photopolymerization initiator were added to the obtained dispersion, and planetary mixing (500 rpm, 1 minute), ultrasonic stirring (1 minute), and degassing (200 rpm, 1 minute) were carried out in this order to prepare a photocurable aqueous slurry.
The water-soluble acrylate used was 4-HBA represented by the above formula (1) or PEGDA represented by the above formula (2). The contents of 4-HBA and PEGDA in the photocurable aqueous slurry were 5.0 mass %, 7.5 mass %, and 10 mass %, respectively, relative to _SiO2 .
The photopolymerization initiator used was 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (ultraviolet light polymerization initiator: UV light 365 nm curing type) or 2,2'-azobis[2-methyl-n-(2-hydroxyethyl)propionamide] (blue light polymerization initiator: blue light 405 nm curing type). The ultraviolet light polymerization initiator was added so that it accounted for 2% by mass relative to the water-soluble acrylate. The blue light polymerization initiator was also added so that it accounted for 2% by mass relative to the water-soluble acrylate.

<Experimental Example 2>
-Evaluation of shear rate and slurry viscosity-
The viscosity curve of each of the photocurable water-based slurries prepared in Experimental Example 1 was measured as follows.
・Method for measuring viscosity curve:
A viscosity curve was measured by using a rheometer equipped with a cone-and-plate jig to continuously measure the apparent viscosity while increasing the shear rate from 0 to 80 s ⁻¹ and decreasing it from 80 to 0 s ⁻¹ .
FIG. 1 is a graph showing the evaluation results of a photocurable aqueous slurry prepared using 4-HBA as the water-soluble acrylate and the above ultraviolet photopolymerization initiator as the polymerization initiator.
FIG. 2 is a graph showing the evaluation results of a photocurable aqueous slurry prepared using 4-HBA as the water-soluble acrylate and the above blue light polymerization initiator as the polymerization initiator.
FIG. 3 is a graph showing the evaluation results of a photocurable aqueous slurry prepared using PEGDA as the water-soluble acrylate and the above-mentioned ultraviolet photopolymerization initiator as the polymerization initiator.

1 to 3, no hysteresis was observed in any of the photocurable aqueous slurries prepared in Experimental Example 1 during the process of increasing the shear rate from 0 to 80 s ^-1 and during the process of decreasing the shear rate from 80 to 0 s ^-1 , indicating that they had excellent dispersion stability.

<Experimental Example 3>
- Evaluation of light curing time and storage modulus -
Each of the photocurable aqueous slurries prepared in Experimental Example 1 was irradiated with ultraviolet light or blue light, and the storage modulus was measured before and after the irradiation as follows.
Measurement of storage modulus:
The storage modulus was measured by dynamic viscoelasticity measurement (frequency 1.0 Hz, strain 0.1%) using a rheometer equipped with a cone-and-plate jig. 30 seconds after the start of the dynamic viscoelasticity measurement, the slurry was irradiated with ultraviolet or blue light for 30 seconds, and the change in storage modulus of the slurry over time was measured.
FIG. 4 is a graph showing the evaluation results of a photocurable aqueous slurry prepared using 4-HBA as the water-soluble acrylate and the above ultraviolet photopolymerization initiator as the polymerization initiator.
FIG. 5 is a graph showing the evaluation results of a photocurable aqueous slurry prepared using 4-HBA as the water-soluble acrylate and the above blue light polymerization initiator as the polymerization initiator.
FIG. 6 is a graph showing the evaluation results of a photocurable aqueous slurry prepared using PEGDA as the water-soluble acrylate and the above-mentioned ultraviolet photopolymerization initiator as the polymerization initiator.

Figures 4 to 6 show that the storage modulus of all of the photocurable aqueous slurries prepared in Experimental Example 1 increased significantly immediately after irradiation with ultraviolet light or blue light, demonstrating that photocuring was possible even with a very small amount of water-soluble acrylate added, less than 10% by mass relative to the inorganic particles.

Claims (4)

(1) inorganic particles; (2) polyalkyleneimine or modified polyethyleneimine having a structure in which a compound having a polyethylene glycol chain is added to polyethyleneimine; (3) water-soluble acrylate; and (4) a photopolymerization initiator ,
The photocurable aqueous slurry has a content of the water-soluble acrylate of 1.5% by mass to 10.0% by mass relative to the inorganic particles . The photocurable aqueous slurry according to claim 1, wherein the weight-average molecular weight of the polyalkyleneimine and the modified polyethyleneimine is 300 to 50,000. The photocurable aqueous slurry according to claim 1, wherein the content of the inorganic particles is 10% to 65% by volume. (5) The photocurable aqueous slurry according to any one of (1) to (3) , further comprising a dispersant which is an anionic polymer.