JP2020007614A - Aqueous iron particle dispersion, method for producing same, and inkjet ink - Google Patents

Abstract

To provide an aqueous iron particle dispersion which is suppressed in oxidation of iron particles.SOLUTION: An iron particle dispersion is obtained by dispersing iron particles, which have an average particle diameter d50 of from 5 nm to 250 nm (inclusive) as determined by a dynamic light scattering method, into water that contains at least one reductant selected from acetyl tocopherol, urine acid, gallic acid, glutathione, glycine, glycyl glycine, L-cysteine hydrochloride, and a dispersant.SELECTED DRAWING: None

Description

  The present invention relates to an aqueous dispersion of iron particles in which fine iron particles are dispersed in water, a method for producing the same, and an ink-jet ink using the aqueous dispersion of iron particles.

With the miniaturization and thinning of electronic devices, fine placement technology and thin film formation technology of metal materials are being studied. I have. In such a printed electronics manufacturing technique, a metal nanoink in which metal nanoparticles having an average particle size of 100 nm or less are dispersed in a solvent is prepared, and is applied and formed into a fine pattern by an inkjet printing method or a screen printing method. Unlike the bulk metal, the metal fine particles have a small particle size, so they are not only suitable for a fine pattern, but also exhibit characteristics such as a decrease in the melting point as the particle size decreases. Therefore, processing at a low temperature lower than the melting point of bulk metal is also expected, and its application to various industrial materials is expected to be promising.
Many studies have been made on silver fine particles and copper particles as the metal used for the metal nanoink. For example, Patent Document 1 proposes a metal nanoparticle ink using copper fine particles. In the case of the ink applied to the inkjet printing method, if the average dispersed particle size of the metal fine particles exceeds 500 nm, clogging of the inkjet head nozzles or the like occurs, and therefore, the average dispersed particle size is preferably 300 nm or less for stable printing. It has been. However, in actuality, there is a technical problem that the surface energy increases due to the progress of fine particles and metal fine particles are easily aggregated, and as the fine particles are formed, a discharge error due to clogging of the aggregated particles in the inkjet nozzle may be caused. There is concern.
In addition, formic acid is mainly used for the ink described in Patent Document 1, but from the viewpoint of reducing both the burden on the working environment and the burden on the global environment, water is required as the main solvent used in the metal nanoink. I have. However, it is known that water easily oxidizes the metal surface and as the particle size increases, the reactivity on the metal surface further increases, the oxidation is promoted and metal oxide is formed, and the characteristics of the metal itself change. . In particular, iron, which has many industrial uses, is more easily oxidized than silver or copper, and it has been difficult to produce a stable aqueous dispersion of iron nanoparticles.
Patent Literature 2 discloses a method of coating the surface of metal fine particles with an organic compound having a 1,2,3 triazole group as a method for preventing oxidation of metal fine particles in an aqueous dispersion.

JP 2008-13466 A JP 2007-270264 A

However, merely adding an organic compound having a 1,2,3 triazole group as described in Patent Literature 2 may not have a sufficient effect of dispersing iron fine particles in water.
An object of the present invention is to provide an aqueous dispersion of iron fine particles in which oxidation of iron fine particles is suppressed, and further to provide an inkjet ink using the aqueous dispersion of iron fine particles.

A first aspect of the present invention is an iron fine particle aqueous dispersion in which iron fine particles are dispersed using water as a dispersion medium,
The average particle diameter d50 of the iron fine particles by a dynamic light scattering method is 5 nm or more and 250 nm or less,
The dispersion medium contains at least one reducing agent selected from acetyltocophenol, uric acid, gallic acid, glutathione, glycine, glycylglycine, and L-cysteine hydrochloride, and a dispersant.
The second step of the present invention is a reduction step of adding a reducing solution containing a first reducing agent to a raw material solution containing a metal salt containing an iron element as a metal, and reducing the metal salt to obtain iron fine particles. When,
A dispersion step of dispersing the iron fine particles obtained in the reduction step with water as a dispersion medium,
In the dispersion step, the dispersion medium contains a dispersant,
During the dispersion step or after the dispersion step, acetyl tocophenol, uric acid, gallic acid, glutathione, glycine, glycylglycine, at least one second reducing agent selected from L-cysteine hydrochloride is added to the dispersion medium. It is a method for producing an aqueous dispersion of iron fine particles, which is characterized by being added.
A third aspect of the present invention is an ink jet ink containing an aqueous dispersion of iron fine particles.

  According to the present invention, oxidation of iron fine particles is suppressed in an iron fine particle aqueous dispersion in which iron fine particles having an average particle diameter d50 determined by a dynamic light scattering method of 5 nm or more and 250 nm or less are well dispersed in water. Therefore, by using the aqueous dispersion of iron fine particles of the present invention, it is possible to provide an inkjet ink in which clogging of iron fine particles in an inkjet nozzle is suppressed and a discharge error is reduced.

It is a flowchart showing an example of a modeling process of a three-dimensional object using an inkjet ink of the present invention. FIG. 2 is a diagram illustrating an outline of a modeling apparatus for modeling a three-dimensional object using the inkjet ink of the present invention.

In general, there are a plurality of methods for dispersing particles. Since the surface area in contact with the dispersion medium is increased by atomizing the particles, the wettability with the dispersion medium is increased and the dispersion can be stabilized. In addition, there is a method of stabilizing dispersion by introducing a dispersant or a dispersing group to the particle surface, thereby imparting electrostatic repulsion or steric repulsion to the particle, and dispersing and stabilizing the particle by combining these methods. be able to. However, when iron particles are atomized and dispersed in water, the reactivity with water increases due to an increase in surface area, and oxidation is promoted. Such water is easy oxidation of the metal can be described by the standard oxidation-reduction potential, precious metal such as silver or copper is a positive value (silver ^{E 0 = + 0.7991 [V]} , copper E ⁰ = +0.340 [V]), so it is not easily oxidized in water. However, since iron is E ⁰ = −0.440 [V], iron is easily oxidized in water, and it is considered that an increase in surface area due to atomization further promotes oxidation to become iron oxide. Although it was improved by the use of a dispersant or the introduction of a dispersing group into the iron fine particles, it was found that oxidation was caused by long-term storage.

  The present invention and the like have found that the use of a specific reducing agent can suppress the oxidation of iron fine particles in water and stabilize the dispersion, and have accomplished the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the following embodiments, and may be appropriately modified based on ordinary knowledge of a person skilled in the art without departing from the spirit of the present invention. Modifications and the like are also included in the scope of the present invention.

  The aqueous dispersion of iron fine particles of the present invention is obtained by dispersing fine iron fine particles having an average particle diameter d50 of 5 nm or more and 250 nm or less by dynamic light scattering (DLS) using water as a dispersion medium. In the present invention, the aqueous iron particle dispersion has an average particle diameter d50 of 5 nm or more and has a surface area capable of maintaining an antioxidant effect, and an average particle diameter of 250 nm or less has a specific gravity capable of maintaining a dispersed state. In the present invention, such a dispersion medium contains at least one reducing agent selected from acetyltocophenol, uric acid, gallic acid, glutathione, glycine, glycylglycine, and L-cysteine hydrochloride, and a dispersant. It is characterized by.

(Reducing agent)
In the present invention, the reducing agent contained in the dispersion medium for dispersing the iron fine particles is at least one selected from acetyltocophenol, uric acid, gallic acid, glutathione, glycine, glycylglycine, and L-cysteine hydrochloride. The amount of the reducing agent should be as large as possible as long as the concentration is below the saturation concentration. May be caused. Therefore, the content is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, and desirably 0.01 to 0.05% by mass, in an ink jet ink or an aqueous dispersion of iron fine particles described later. Further, the reducing agent is preferably contained in an amount of 0.01 to 30 parts by mass, more preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the iron fine particles.

(Dispersant)
In the present invention, the dispersant to be contained in the dispersion medium for dispersing the iron fine particles may be any of a water-soluble resin and a surfactant, but in the present invention, the dispersion medium is water. Of the nature is used. Preferably, it is at least one selected from unsaturated fatty acids, dodecyl sulfate, dodecyl benzene sulfonic acid, salts thereof, and water-soluble polymers. Among them, unsaturated fatty acids and salts thereof are preferable, and as such unsaturated fatty acids, monounsaturated fatty acids having 14 to 24 carbon atoms are preferable. Specific examples include myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, gadolinic acid, eicosenoic acid, erucic acid, and nervonic acid. The counter ions of these unsaturated fatty acid salts are preferably sodium, potassium and ions of the compound represented by the following general formula (1).

上記式（１）において、Ｒ₁、Ｒ₂、Ｒ₃はそれぞれ独立に、−Ｈ、−ＣＨ₃、−ＣＨ₂ＣＨ₃、−ＣＨ₂ＣＨ₂ＣＨ₃、−ＣＨ₂ＣＨ₂ＣＨ₂ＣＨ₃、−ＣＨ₂ＯＨ、−ＣＨ₂ＣＨ₂ＯＨ、−ＣＨ₂ＣＨ₂ＣＨ₂ＯＨのいずれかである。
上記のような有機アミン系のカウンターイオンを用いた場合、加熱・焼結によって除去可能であるため、鉄の金属としての性能をより大きく発現することが可能となる。

In the above formula (1), R ₁ , R ₂ , and R ₃ are each independently -H, -CH ₃ , -CH ₂ CH ₃ , -CH ₂ CH ₂ CH ₃ , -CH ₂ CH ₂ CH ₂ CH ₃ is either _{-CH 2 OH, -CH 2 CH 2} OH, -CH 2 CH 2 CH 2 OH.
When an organic amine-based counter ion as described above is used, it can be removed by heating and sintering, so that the performance of iron as a metal can be exhibited more greatly.

  Further, as the water-soluble polymer, an acrylic polymer, a polyurethane-based polymer, a polyalkylene polyamine, a polyethylene imine, or the like is preferably used.

The dispersant is preferably contained in the aqueous dispersion of iron fine particles in an amount of 0.1 to 20% by mass, more preferably 1 to 10% by mass. When the dispersant is 0.1% by mass or more, the effect of dispersing the iron fine particles is obtained, and the effect of suppressing oxidation is also obtained. When the content is 20% by mass or less, the viscosity is also in an appropriate range.
In the present invention, other dispersants may be further added as long as they do not cause the disruption of the aqueous dispersion of iron fine particles.

〔Production method〕
Hereinafter, the method for producing the aqueous iron particle dispersion of the present invention will be described.
The method for producing metal fine particles is roughly classified into a physical method and a chemical method. The physical method is a method of pulverizing a large lump into small pieces and is suitable for mass production, but it is difficult to control the size and shape. In addition, the chemical method is a method in which metal ions are produced by reduction of metal ions in water or the like, and a substance having a desired size and structure can be produced. The iron fine particles used in the aqueous dispersion of iron fine particles of the present invention may be prepared by any of a physical method and a chemical method, but there is no problem. However, in order to control the particle diameter, it is preferable to prepare the fine particles by a chemical method. Hereinafter, a method for producing iron fine particles by a chemical method will be described.

  The method for producing the aqueous dispersion of iron fine particles of the present invention by a chemical method comprises a reduction step and a dispersion step. In the reduction step, a reducing solution containing the first reducing agent is added to a raw material solution containing an iron element as a metal to obtain iron fine particles, and in the dispersing step, the iron fine particles obtained in the reducing step are mixed with Water containing the two reducing agents is dispersed as a dispersion medium.

<Reduction process>
(A) Preparation of Raw Material Solution and Reduction Solution A metal salt (iron salt) containing an iron element as a metal is completely dissolved in deionized water or / and alcohols to obtain a raw material solution. The concentration of the iron salt in the raw material solution is preferably 0.1 to 20% by mass. Separately, the first reducing agent is completely dissolved in deionized water or / and alcohols to obtain a reduced solution. The amount of the first reducing agent is preferably 1 to 20 times the molar concentration of the iron salt used.

  Iron fine particles can be obtained by reduction from an iron salt. The iron salt used in the present invention may be any of Fe (II) salt and Fe (III) salt, and the counter anion is not limited as long as it dissociates into ions in water. For example, iron (II) chloride, iron (III) chloride, iron (II) bromide, iron (II) sulfate, iron (III) nitrate, iron (II) acetate, iron (III) acetate, iron acetylacetonate and the like Is mentioned.

  As the first reducing agent, a reducing agent generally used for reducing a metal can be used. Examples include sodium borohydride, lithium borohydride, sodium hydride, lithium hydride, hydrazine, ascorbic acid, and the like. The higher the reducing agent concentration, the more preferable it is a saturated solution at room temperature at 1% by mass or more.

  Deionized water and alcohols are mainly used as the solvent for the raw material solution and the reducing solution. The alcohols include, for example, methanol, ethanol, propanol, isopropanol and the like, and one or more kinds thereof may be used, or may be used by mixing with deionized water. Further, a water-soluble solvent may be added. Examples of the water-soluble solvent include glycerin, ethylene glycol, diethylene glycol, diglycerol, polyethylene glycol, and the like. One or more kinds may be used, or a mixture of deionized water and alcohols may be used.

In the reduction step, by using a specific control agent, it is possible to control the shape and the particle size of the iron fine particles generated by the reduction. It is considered that the reason is that these control agents are adsorbed on the crystal surface growing by the reducing agent, thereby inhibiting crystal growth and suppressing the primary particle size of the iron fine particles.
Examples of such a control agent include polyethylene glycol (PEG), a pyrrolidone compound represented by the following general formula (2), polyvinyl pyrrolidone (PVP), and a vinyl pyrrolidone copolymer (PVP copolymer).

上記式（２）において、Ｒ₄は、−Ｈ、−ＣＨ₃、−ＣＨ₂ＣＨ₃、−ＣＨ₂ＯＨ、−ＣＨ₂ＣＨ₂ＯＨのいずれかである。

In the above formula (2), R ₄ is any of —H, —CH ₃ , —CH ₂ CH ₃ , —CH ₂ OH, and —CH ₂ CH ₂ OH.

  Examples of the pyrrolidone compound include 2-pyrrolidone, N-methylpyrrolidone, N-ethylpyrrolidone, N-methanolpyrrolidone, and N-ethanolpyrrolidone.

  The weight average molecular weight of PVP or PVP copolymer contained as a control agent is preferably in the range of 1,000 to 100,000. In addition, by mixing a plurality of PVPs having different molecular weight distributions and adding them with a wide molecular weight distribution, they can interact with various crystal planes and suppress an increase in the particle diameter of the iron fine particles.

The control agent may be added to either the raw material solution or the reducing solution. However, since the reducing solution is desirably a high-concentration solution of the reducing agent itself, it is preferably added to the raw material solution. The control agent is preferably used in an amount of 20 to 200 parts by mass with respect to 100 parts by mass of the iron salt.
In the present invention, by using the control agent, the average particle diameter d50 of the iron fine particles in the aqueous iron fine particle dispersion can be controlled to 200 nm or less.

(B) Reduction It is desirable to carry out the reduction in an inert gas atmosphere in order to suppress the oxidation reaction of the precipitated iron fine particles. As the inert gas, an inert gas such as nitrogen or argon is preferable. The raw material solution is stirred while being heated in a water bath at 30 to 70 ° C., and the reduced solution is dropped into the raw material solution at a rate of 0.05 to 5.0 mL / sec. Immediately after dropping, a black iron fine particle suspension is obtained. The reaction is preferably performed for a time sufficient to obtain a suspension.

(C) Washing After the reduction, the suspension is washed with deionized water. As a washing method, any method such as decantation, centrifugation, and ultrafiltration can be used. Since the iron fine particles have magnetism, a method of performing adsorption and decantation by a magnet is simple. The washing is performed until the concentration of the reducing agent or the constituent element of the reducing agent contained in the removed solution becomes 100 ppm or less. After washing, a high-concentration iron fine particle paste is obtained.

<Dispersion process>
A dispersing agent, a second reducing agent, and a solvent are added to the iron fine particle paste obtained in the reduction step, and after sufficient stirring, the iron fine particles are dispersed. The dispersion is performed by a method such as ultrasonic stirring, an ultrasonic homogenizer, a jet mill, a bead mill, a homogenizer, a nanomizer, or a combination of these methods. The dispersion conditions are not particularly limited and vary depending on the apparatus actually used. However, depending on the type of iron particles to be treated, the concentration, the type of the dispersant, the concentration, and the like, a uniform dispersion can be formed according to the treatment amount. May be set appropriately.

  In such a step, the iron fine particles may react with water and become oxidized due to the reduced particle size, but in the present invention, the above-mentioned oxidation can be suppressed by using the second reducing agent. . The second reducing agent is preferably added during the dispersing step, but it may be considered that the second reducing agent may be added after the dispersing step depending on the difference in the adsorption ability between the dispersant and the iron fine particles.

[Inkjet ink]
The aqueous dispersion of iron fine particles of the present invention is preferably applied to an inkjet ink (hereinafter, referred to as “ink”). Such an ink may contain a water-soluble organic solvent, a surfactant, resin particles, and additives, in addition to the aqueous iron particle dispersion of the present invention. These additions make it possible to impart ink jet suitability to the aqueous dispersion of iron fine particles. The viscosity, surface tension, and pH, which are the liquid properties of the ink, may be appropriately adjusted by the above-mentioned water-soluble organic solvent, surfactant, resin particles, and additives according to the inkjet head to be used.

<Water-soluble organic solvent>
The ink of the present invention contains water and a water-soluble organic solvent. Water is included as a dispersion medium for the aqueous dispersion of iron fine particles of the present invention, but deionized water (ion-exchanged water) may be added separately. The content of water in the ink is preferably from 10 to 90% by mass.

The “water-soluble organic solvent” used in the present invention means “an organic solvent having a solubility in water at 20 ° C. of 500 g / L or more”. As the water-soluble organic solvent, any of those known as usable in inks can be used. Examples include alcohols, glycols, alkylene glycols, polyethylene glycols, nitrogen-containing compounds, sulfur-containing compounds, and the like. Specific examples include glycerin, ethylene glycol, diethylene glycol, polyethylene glycol having a weight average molecular weight of 10,000 or less, 1,3-propanediol, 1,4-butanediol, diglycerol, and 2-pyrrolidone. One or more of these water-soluble organic solvents can be used as necessary.
The content of the water-soluble organic solvent in the ink is preferably 50% by mass or less, more preferably 5% by mass or more and 45% by mass or less, and particularly preferably 5% by mass or more and 30% by mass or less.

<Surfactant>
The ink of the present invention can include a surfactant. As the surfactant, any of conventionally known surfactants can be used, and among them, ethylene oxide adducts such as acetylene glycol which are nonionic surfactants, fluorine surfactants, and silicon surfactants are preferable. Among them, it is more preferable to use an ethylene oxide adduct such as acetylene glycol and a fluorine-based surfactant.
Examples of ethylene oxide adducts such as acetylene glycol include Surfynol 104, 440, and 465 (all manufactured by Air Products), acetylenols E40, E60, and E100 (all manufactured by Kawaken Fine Chemical) and Dynol 604, 607, 800, and 810. (Above, manufactured by Air Products).
Examples of the fluorine-based surfactant include FS-3100, FS-30, FSN-100 (manufactured by DuPont), Megafac F-444 (manufactured by DIC), and DSN403N (manufactured by Daikin Industries, Ltd.).

  The content of the surfactant is preferably 0.1 to 3.0% by mass in the ink, more preferably 0.2 to 1.5% by mass. At 0.1% by mass or more, a sufficiently large dot diameter can be obtained and the drawing portion can be satisfactorily buried. At 3.0% by mass or less, iron fine particles penetrate deeply into the recording medium and iron concentration is locally increased. Can be suppressed.

  These surfactants may be added in combination of two or more. In particular, by combining an ethylene oxide adduct such as acetylene glycol with a fluorine-based surfactant or a silicon-based surfactant, an effect of increasing the dot diameter can be obtained.

<Additive>
In the ink of the present invention, if necessary, various surfactants other than the above, a pH adjuster, a rust inhibitor, a preservative, a fungicide, an antioxidant, an evaporation accelerator, and a chelating agent. Additives may be added. As the pH adjuster, it is preferable to use an amine compound having a buffering ability, and it is particularly preferable to use N-butyldiethanolamine.

(3D object modeling)
The ink of the present invention can be used in a modeling process in a modeling apparatus called an additive manufacturing (AM) system, a three-dimensional printer, a rapid prototyping system, or the like. The molding process of a three-dimensional object using the ink of the present invention utilizes a feature of metal fine particles that the melting point decreases as the particle size decreases, and becomes more prominent in nanoparticles having a size of about several tens nm or less. It is. The iron fine particles contained in the ink of the present invention have an average particle diameter d50 of 250 nm or less, and the particle diameter can be controlled to be smaller. Therefore, by using in combination with particles having an average particle diameter of 1 μm or more and having a large particle diameter, the above-described molding process can be performed. Hereinafter, an embodiment of a three-dimensional object forming process using the ink of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view in the thickness direction of a powder layer 11 described later.

The three-dimensional object forming process of this example includes the following steps.
Step 1: Form a powder layer containing stainless steel particles.
Step 2: The ink of the present invention is applied to the modeling region of the powder layer.
Step 3: Iron fine particles contained in the ink are sintered to fix the stainless steel particles in the molding region.
Step 4: Remove stainless particles outside the modeling region.

<Step 1>
A powder layer 11 containing stainless particles is formed based on the slice data acquired in advance (FIG. 1A). The slice data is data obtained by slicing the three-dimensional shape of the modeling object at a predetermined interval (thickness), and is data including information such as a cross-sectional shape, a layer thickness, and a material arrangement.

  The average particle size of the stainless steel particles is preferably set to a size that does not cause aggregation in order to form the powder layer 11 well. Further, it is preferable that the average particle diameter is set to a size suitable for diffusion of the ink 12 applied in the step 2, fixing of the stainless steel particles in the heat treatment in the step 3, and further, demand for strength and function of the three-dimensional object. Specifically, the volume average particle diameter of the stainless steel particles may be selected from the range of 1 μm or more and 500 μm or less, and preferably selected from the range of 1 μm or more and 100 μm or less. When the average particle diameter is 1 μm or more, aggregation of particles during the formation of the powder layer 11 is suppressed, and a layer with few defects tends to be easily formed.

  The average particle size of the stainless steel particles is measured using a laser diffraction / scattering particle size distribution analyzer “LA-950” (manufactured by HORIBA). The attached dedicated software is used for setting the measurement conditions and analyzing the measurement data. As a specific measuring method, first, a batch type cell containing a measuring solvent (organic solvent) is set in a laser diffraction / scattering type particle size distribution measuring apparatus “LA-950” (manufactured by HORIBA) and the optical axis is measured. Adjust and adjust the background. The powder to be measured is added to the batch-type cell until the transmittance of the tungsten lamp becomes 95% to 90%, the particle size distribution is measured, and the volume-based average particle size is calculated from the obtained measurement results. .

<Step 2>
Based on the slice data of the modeling object, the ink 12 of the present invention is applied to the modeling region of the powder layer 11 made of stainless steel particles by an ink jet device, and dried if necessary (FIG. 1B).

  The iron fine particles contained in the ink 12 of the present invention have an average particle size d50 of 250 nm or less, which is significantly smaller than the average particle size of the stainless particles forming the powder layer 11. Therefore, the sintering or melting start temperature of the iron fine particles contained in the ink 12 is lower than the sintering or melting start temperature of the stainless steel particles. Therefore, in Step 3, the stainless steel in the region where the ink 12 is applied is heated to a temperature lower than the sintering or melting start temperature of the stainless steel particles and higher than the sintering or melting start temperature of the iron fine particles contained in the ink 12. Particles can be fixed to each other via iron fine particles.

<Step 3>
The ink 12 is heated to a temperature lower than the sintering or melting start temperature of the stainless particles and higher than the sintering or melting start temperature of the iron fine particles contained in the ink 12. Thus, the stainless steel particles in the region to which the ink 12 has been applied are fixed via the iron fine particles contained in the ink 12 (FIG. 1C). Reference numeral 13 in FIG. 1C indicates a region where the stainless steel particles are fixed via the iron fine particles.

  As shown in FIGS. 1D to 1F, the above steps 1 to 3 are repeated to form a laminate 14 containing a target three-dimensional object therein (FIG. 1 (g)).

  In this example, the example in which the steps 1 to 3 are repeated to obtain the laminated body 14 is shown. However, after the steps 1 to 2 are repeated, the laminated body 14 can be obtained by performing the step 3 once. It is.

<Step 4>
The three-dimensional object 15 is obtained by removing the stainless particles other than the modeling region from the laminate 14 (FIG. 1 (h)). Since the stainless steel particles in the area where the ink 12 has not been applied in the step 2 are not fixed even after the step 3, they can be easily removed in this step. After this step, the entire three-dimensional object 15 may be heated at a temperature higher than the heating temperature in step 3 to sinter the stainless particles.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples at all unless it exceeds the gist thereof.

(Examples 1 to 28, Comparative Examples 1 to 6)
Control agents, dispersants, and reducing agents used in the following Examples and Comparative Examples are as follows.

<Control agent>
C-1: PEG1000 (Mw: 1000)
C-2: PVP K-30 (Mw: 30000)
<Dispersant>
D-1: ammonium oleate D-2: potassium oleate D-3: oleic acid-N-butyldiethanolamine D-4: sodium dodecylbenzenesulfonate D-5: ammonium dodecylbenzenesulfonate D-6: sodium dodecyl sulfate D-7: Sodium polyacrylate D-8: Marialim FA-1150A (aqueous comb polymer manufactured by NOF Corporation)
<Reducing agent>
R-1: Gallic acid R-2: Glutathione oxidized form R-3: Glutathione reduced form R-4: Glycine R-5: Glycylglycine R-6: Uric acid R-7: Acetyl tocophenol R-8: L- Cysteine hydrochloride R-9: DL-α lipoic acid R-10: L-ascorbic acid

3.7 g of FeCl ₂ .4H ₂ O as an iron salt was placed in an eggplant-shaped flask, a control agent was added to a solution containing 50.0 g of ethanol and 50.0 g of deionized water, and the mixture was heated in a water bath at 50 ° C. Thus, a raw material solution was prepared. Next, as a first reducing agent, 1.0 g of NaBH ₄ was added to 2.0 g of deionized water and dissolved to prepare a reducing solution, and 0.1 g / sec of the raw material solution heated to 50 ° C. Dropped at a rate. The raw material solution became a black suspension immediately after the addition of the reducing solution, and iron fine particles were generated. Thereafter, the iron fine particles were sufficiently washed with deionized water, and the process was terminated when the sodium ion concentration of the washing solution became 100 ppm or less, to obtain an iron fine particle paste. According to thermal analysis by TG-DTA, the iron fine particle paste contained 50% by mass or more of iron fine particles, and in the example using the control agent, contained 0.1% by mass of the control agent.

  10 g of deionized water, a dispersant and a second reducing agent were added to the iron fine particle paste, and the mixture was stirred at room temperature for 30 minutes. The deionized water was used after gas replacement by bubbling nitrogen gas for 30 minutes or more. Thereafter, the iron fine particles were dispersed with a homogenizer T-25 (manufactured by IKA) at 8,600 rpm for 1 hour to obtain an aqueous dispersion of iron fine particles. About the obtained iron fine particle aqueous dispersion, the average particle diameter d50 was measured and oxidized by the following methods. Tables 1 to 3 show the types and amounts [g] of the iron salt, the control agent, the dispersant, and the second reducing agent used.

<Measurement of average particle size d50>
The measurement was performed three times for 180 seconds using a particle diameter measuring device Nanotrac 150 (manufactured by Microtrac Co., Ltd.) by the DLS method, and the average particle diameter d50 was obtained. Table 4 shows the results.
<Oxidation evaluation>
The aqueous dispersions of iron fine particles of Examples and Comparative Examples were allowed to stand at room temperature, and after one day and three days, a state of 100-fold dilution with deionized water was visually observed, and the degree of oxidation was evaluated according to the following criteria. Table 4 shows the results.
○: Gray or black ×: Reddish or other colors

(Example 29)
37 g of FeCl ₂ .4H ₂ O was placed in an eggplant-shaped flask, and 20 g of PVP K-30, 500 g of ethanol and 500 g of deionized water were added and dissolved to prepare a raw material solution. Further, 10 g of NaBH ₄ as a first reducing agent was added to and dissolved in 20 g of deionized water to prepare a reducing solution.

  Subsequently, the raw material solution was heated while being stirred at 400 rpm by a forced stirrer in a water bath at 50 ° C., and after the solution temperature reached 50 ° C., the reduced solution was added to the raw material solution at a rate of 0.1 g / sec. Was dropped. The raw material solution immediately became a black suspension solution after the addition of the reducing solution, and iron fine particles were generated. Thereafter, the iron fine particles were sufficiently washed with deionized water, and the process was terminated when the sodium ion concentration of the washing solution became 100 ppm or less, to obtain an iron fine particle paste. According to a thermal analysis using a thermogravimetric differential thermal analyzer (TG-DTA) (manufactured by Rigaku Corporation), the iron fine particle paste contained 50% by mass or more of iron fine particles and 0.1% by mass of PVP.

  To the iron fine particle paste, 10.0 g of ammonium oleate, 30 g of deionized water, and 0.5 g of gallic acid were added and stirred at room temperature for 30 minutes. Thereafter, iron particles were dispersed with a homogenizer ("T-25" manufactured by IKA) at 8,600 rpm for 1 hour to obtain an aqueous dispersion of iron particles. The obtained aqueous dispersion of iron fine particles was mixed with the following composition, stirred for 60 minutes, and then passed through a filter to prepare an ink for an inkjet apparatus.

<Ink composition>
Aqueous dispersion of iron fine particles 79 parts by weight Glycerin 5 parts by weight Diethylene glycol 5 parts by weight PEG1000 (Mw: 1000) 10 parts by weight Acetylenol E100 1 part by weight

The average particle size d50 of the iron fine particles contained in the obtained inkjet ink was 86 nm, and no oxidation was confirmed. In addition, 10 mg of the aqueous dispersion of iron fine particles was put into a platinum pan by TG-DTA, and analyzed at 900 ° C. (heating rate: 10 ° C./min) in an air flow. From the final residue, the concentration (% by mass) of the iron fine particles was determined. At this time, it was assumed that all organic substances had evaporated, and that all iron had changed to iron oxide (Fe ₃ O ₄ ), and 69% of the residue was calculated as an iron component. The iron concentration in the ink was 5.0 mass%. %Met. The obtained ink was ejected using a drawing apparatus equipped with a piezo head “KJ4B” (manufactured by Kyocera), and it was confirmed that a pattern could be drawn.

(Example 30)
A three-dimensional object was formed using the ink obtained in Example 29 and SUS particles having a volume average particle diameter of 30 μm. FIG. 2 shows an outline of the molding apparatus used in this example. In the modeling apparatus of FIG. 2, a powder supply device 201 for supplying SUS particles on a shaft having a transport motor 103, a roller 202 for leveling the supplied powder, and an application device 203 for applying ink are movably installed. I have. After powder containing one layer of SUS particles was supplied from the powder supply device 201 to the 200 mm × 200 mm modeling stage 101, the powder was leveled by the roller 202 to form a powder layer 301 having a thickness of 2 mm. The ink adjusted in Example 29 was applied to the formed powder layer 301 in a range of 10 mm × 10 mm according to the shape of the modeled object to be formed by the application device 203 until the penetration depth became 2 mm. After the ink application, the modeling stage 101 was lowered by one layer, and powder containing SUS particles was supplied again to form a powder layer 301 of 200 mm × 200 mm and 2 mm in thickness. The ink was applied to the area of 20 mm × 10 mm by the applicator 203 until the penetration depth became 2 mm so that the center of gravity coincided with the area to which the ink was previously applied.

  The obtained laminate was put into an electric furnace together with the molding stage 101 so as not to lose its shape, and heat-treated at a temperature equal to or higher than the sintering start temperature of iron nanoparticles and lower than the sintering start temperature of SUS particles for 1 hour. After the heat treatment, the powder in the portion A of the laminate where the ink was applied was solidified. Observation with a microscope revealed that the SUS particles were fixed by iron fine particles existing between the particles. By removing the powder in the portion where the ink was not applied, a desired molded product could be obtained. The obtained shaped article had an overhang structure in which the second layer was larger than the first layer, and no particular shape distortion was observed.

Claims (20)

An iron particle aqueous dispersion in which iron particles are dispersed using water as a dispersion medium,
The average particle diameter d50 of the iron fine particles by a dynamic light scattering method is 5 nm or more and 250 nm or less,
The iron, wherein the dispersion medium contains at least one reducing agent selected from acetyltocophenol, uric acid, gallic acid, glutathione, glycine, glycylglycine, and L-cysteine hydrochloride, and a dispersant. Fine particle aqueous dispersion.   The aqueous dispersion of iron fine particles according to claim 1, wherein the reducing agent is gallic acid.   3. The aqueous dispersion of iron particles according to claim 1, wherein the reducing agent is contained in an amount of 0.01 to 30 parts by mass with respect to 100 parts by mass of the iron particles.   4. The aqueous dispersion of iron particles according to claim 1, wherein the dispersant is contained in the aqueous dispersion of iron particles at 0.1 to 20% by mass. 5.   The method according to any one of claims 1 to 3, wherein the dispersant contains at least one selected from unsaturated fatty acids, dodecyl sulfate, dodecyl benzene sulfonic acid, salts thereof, and water-soluble polymers. An aqueous dispersion of iron fine particles according to the above.   The aqueous dispersion of iron particles according to claim 5, wherein the dispersant is at least one selected from monounsaturated fatty acids having 14 to 24 carbon atoms and salts thereof.   The monounsaturated fatty acid is at least one selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, gadolinic acid, eicosenoic acid, erucic acid, and nervonic acid. Item 7. An aqueous dispersion of iron fine particles according to Item 6. 8. The iron fine particles according to claim 6, wherein the counter ion of the monounsaturated fatty acid salt is any one of sodium, potassium, and a compound represented by the following general formula (1). 9. Water dispersion.

[In the above formula (1), R ₁ , R ₂ , and R ₃ are each independently —H, —CH ₃ , —CH ₂ CH ₃ , —CH ₂ CH ₂ CH ₃ , —CH ₂ CH ₂ CH ₂ CH _3, it is either _{-CH 2 OH, -CH 2 CH 2} OH, -CH 2 CH 2 CH 2 OH. ] 9. The dispersion medium according to claim 1, wherein the dispersion medium contains at least one kind of a control agent selected from a pyrrolidone compound represented by the following general formula (2), polyvinylpyrrolidone, a vinylpyrrolidone copolymer, and polyethylene glycol. The aqueous dispersion of iron fine particles according to any one of the above.

[In the above formula (2), R ₄ is any one of —H, —CH ₃ , —CH ₂ CH ₃ , —CH ₂ OH, and —CH ₂ CH ₂ OH. ] A reduction step of adding a reducing solution containing a first reducing agent to a raw material solution containing a metal salt containing iron element as a metal, and reducing the metal salt to obtain iron fine particles,
A dispersion step of dispersing the iron fine particles obtained in the reduction step with water as a dispersion medium,
In the dispersion step, the dispersion medium contains a dispersant,
During the dispersion step or after the dispersion step, acetyl tocophenol, uric acid, gallic acid, glutathione, glycine, glycylglycine, at least one second reducing agent selected from L-cysteine hydrochloride is added to the dispersion medium. A method for producing an aqueous dispersion of iron fine particles, which is added.   The method according to claim 10, wherein the second reducing agent is gallic acid.   The method according to claim 10 or 11, wherein the second reducing agent is added in an amount of 0.01 to 30 parts by mass with respect to 100 parts by mass of the iron fine particles.   The iron according to any one of claims 10 to 12, wherein the dispersant is added to the dispersion medium so as to be included in the aqueous dispersion of iron fine particles in an amount of 0.1 to 20% by mass. A method for producing an aqueous dispersion of fine particles.   The method according to any one of claims 10 to 13, wherein the dispersant comprises at least one selected from unsaturated fatty acids, dodecyl sulfate, dodecyl benzene sulfonic acid, salts thereof, and water-soluble polymers. A method for producing the aqueous dispersion of iron fine particles according to the above.   The method according to claim 14, wherein the dispersant is at least one selected from monounsaturated fatty acids having 14 to 24 carbon atoms and salts thereof.   The monounsaturated fatty acid is at least one selected from myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, gadolinic acid, eicosenoic acid, erucic acid, and nervonic acid. Item 16. The method for producing an aqueous dispersion of iron fine particles according to Item 15. The iron fine particles according to claim 15 or 16, wherein the counter ion of the salt of the monounsaturated fatty acid is any one of sodium, potassium, and a compound represented by the following general formula (3). A method for producing an aqueous dispersion.

[In the above formula (3), R ₁ , R ₂ , and R ₃ are each independently -H, -CH ₃ , -CH ₂ CH ₃ , -CH ₂ CH ₂ CH ₃ , -CH ₂ CH ₂ CH ₂ CH _3, it is either _{-CH 2 OH, -CH 2 CH 2} OH, -CH 2 CH 2 CH 2 OH. ] In the reduction step, at least one of the raw material solution and the reduction solution contains at least one control agent selected from a pyrrolidone-based compound represented by the following general formula (4), polyvinylpyrrolidone, a vinylpyrrolidone copolymer, and polyethylene glycol. The method for producing an aqueous dispersion of iron fine particles according to any one of claims 10 to 17, wherein the aqueous dispersion of iron fine particles is contained.

[In the above formula (4), R ₄ is any one of —H, —CH ₃ , —CH ₂ CH ₃ , —CH ₂ OH, and —CH ₂ CH ₂ OH. ]   19. The method for producing an aqueous dispersion of iron fine particles according to claim 18, wherein the control agent is used in an amount of 20 to 200 parts by mass with respect to 100 parts by mass of the iron salt.   An inkjet ink comprising the iron fine particle aqueous dispersion according to any one of claims 1 to 9.

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