JP2024051992A - Inkjet ink - Google Patents

Abstract

[Problem] To improve the uniformity of film thickness in an inkjet printed area. [Solution] The inkjet ink disclosed herein contains ceramic powder, a binder resin, and an organic solvent. When the average primary particle diameter of the ceramic powder when the ceramic powder dispersed in a dispersion medium is measured by a dynamic scattering method is taken as DP, and the average particle diameter of the ceramic powder when the inkjet ink is measured by the dynamic scattering method is taken as DI, the ratio of the average primary particle diameter DP to the average particle diameter DI (DI/DP) is 1.05 or more and 1.5 or less. The viscosity is 10 (mPa·s) or less. [Selected Figure] None

Description

This disclosure relates to inkjet inks.

Inkjet printing is one printing method for drawing an image on the surface of a printing target. Inkjet printing is used in a variety of fields because it can print high-precision images at low cost and on demand, and causes little damage to the printing target. For example, in recent years, inkjet printing has been used in the manufacture of electronic components. In conventional electronic component manufacturing, electrodes are formed by applying a slurry containing inorganic powder such as metal particles or ceramic particles to the surface of a substrate and firing the substrate. On the other hand, in inkjet printing, instead of applying this slurry, an ink containing inorganic powder is ejected (printed) onto the surface of the substrate to form electrodes.

Electrodes are included in electrochemical cells such as solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs), and proton conductive ceramic fuel cells (PCFCs). For example, SOFCs are known as cells that have the advantage of being highly efficient at generating electricity and being able to use a variety of fuels among various fuel cells. For this reason, development of SOFCs is underway as a next-generation power generation device. This SOFC includes a solid electrolyte, which is a dense layer made of an oxygen ion conductor, a cathode (air electrode) with a porous structure provided on one side of the solid electrolyte, and an anode (hydrogen electrode) with a porous structure provided on the other side of the solid electrolyte. Patent Documents 1 and 2 disclose the formation of electrodes for SOFCs using inkjet printing.

JP 2008-071537 A JP 2010-077463 A

The inventors want to improve the uniformity of the film thickness in the inkjet printed area.

The ink-jet ink disclosed herein includes a ceramic powder, a binder resin, and an organic solvent. When the ceramic powder dispersed in a dispersion medium is measured by a dynamic scattering method, the average primary particle diameter of the ceramic powder is defined as D _P , and when the ink-jet ink is measured by the dynamic scattering method, the average particle diameter of the ceramic powder is defined as D _I , the ratio (D _I /D _P ) of the average primary particle diameter D _P to the average particle diameter D _I is 1.05 or more and 1.5 or less. The viscosity is 10 (mPa·s) or less.

In an inkjet ink of this composition, the ceramic powder is in a moderately aggregated state in the ink. The ink viscosity is also set to an appropriate level. This improves the uniformity of the film thickness in the inkjet printed area.

In a preferred embodiment of the ink-jet ink, the ceramic powder has an average primary particle diameter D _P of 100 nm or more and 500 nm or less. This configuration not only improves the uniformity of the thickness of the printed film, but also suppresses the deterioration of the ink jetting properties.

In another preferred embodiment of the inkjet ink, the content of the ceramic powder is 5% by weight or more and 40% by weight or less when the entire inkjet ink is taken as 100% by weight. This configuration not only improves the uniformity of the film thickness of the printed film, but also increases the efficiency of producing the printed film.

In another preferred embodiment of the ink-jet ink, the ratio (D _I /D _P ) is 1.06 or more and 1.35 or less. With this configuration, the effects of the technology disclosed herein are more effectively realized.

In another preferred embodiment of this inkjet ink, the viscosity of the ink is 7 (mPa·s) or more and 9 (mPa·s) or less. With this configuration, the effects of the technology disclosed herein are more effectively realized.

In another preferred embodiment of the inkjet ink, the ceramic powder is a conductive ceramic powder. This configuration makes it possible to impart electrical conductivity to the fired body of the printed film.

Preferably, the inkjet ink is used to form electrodes of an electrochemical cell. With this configuration, it is possible to provide an electrochemical cell that can perform appropriately.

FIG. 2 is a cross-sectional view that illustrates a typical agitator/pulverizer used in the production of ink. FIG. 2 is a cross-sectional view of an electrochemical cell 200. FIG. 1 is an overall view illustrating an example of an inkjet device. FIG. 4 is a cross-sectional view illustrating a schematic diagram of an ink-jet head of the ink-jet device in FIG. 3.

Below, an embodiment of the technology disclosed herein is described. Note that matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. In this specification, the notation "P to Q" indicating a numerical range includes "P or more and Q or less", "more than P and less than Q", "more than P and Q or less", and "P or more and less than Q".

<Inkjet ink>
The inkjet ink (hereinafter, sometimes simply referred to as "ink") disclosed herein may contain (A) an inorganic powder, (B) a binder resin, and (C) an organic solvent. In the ink, for example, the inorganic powder is dispersed in an organic vehicle component (a mixture of a binder resin and an organic solvent). Each component contained in the ink disclosed herein will be described below.

(A) Inorganic Powder The inorganic powder is a material that constitutes a printed film on a substrate. Here, the "printed film" is a film-like material obtained by applying an ink to a substrate, and is an unfired body. The inorganic powder is a material that constitutes a fired body of the printed film (hereinafter also referred to as a "fired film") (for example, an electrode, etc.) obtained by firing such a printed film. In the ink disclosed here, the inorganic powder may contain ceramic powder as a main component. Herein, "R contains S as a main component" means that when the entire R (for example, the entire inorganic powder) is taken as 100% by weight, the content ratio of S (for example, ceramic powder) is, for example, 50% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more (the closer to 100% by weight, the better). The ceramic powder may be composed of ceramic particles. The ceramic particles may contain unavoidable impurities that may be mixed in during the production process of the ceramic particles, in addition to the ceramic that constitutes the ceramic particles. The ceramic powder may be composed of one type of ceramic powder, or may be composed of two or more types of ceramic powder.

The type of ceramic powder is not particularly limited, as long as it is appropriately set according to the function to be imparted to the fired film formed using the ink disclosed herein. The ceramic powder may be, for example, a conductive ceramic powder. In this case, the ceramic may preferably be, for example, a perovskite oxide represented by the general formula: _ABO3 . The A site of such a perovskite oxide may include, for example, at least one of lanthanoid elements (e.g., lanthanum (La), cerium (Ce), praseodymium (Pr), etc.) and alkaline earth metal elements (e.g., strontium (Sr), barium (Ba), radium (Ra), etc.). The B site may include, for example, at least a transition metal element (e.g., manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), etc.). Among them, the perovskite oxide preferably used may be, for example _, a perovskite oxide containing La, _Sr , and Mn, such as (La,Sr) _MnO3 (e.g., _{La0.8Sr0.2MnO3} ; LSM); or a perovskite oxide containing La, Sr, and Co, such as (La,Sr) _CoO3 (e.g. _{, La0.6Sr0.4CoO3} ; LSC) or (La _, Sr) ₍ Co, _{Fe )} O3 ₍ e.g., _{La0.6Sr0.4Co0.2Fe0.8O3} ; LSCF). By using a conductive ceramic powder as _the ceramic powder, for example, a conductive fired film can be produced. In this case, the various ceramics mentioned herein are also suitable for use in forming electrodes (eg, air electrodes) of electrochemical cells because of their oxide ion conductivity.

Alternatively, the ceramic powder may include non-conductive ceramic powder. In this case, the ceramic may be, for example, a metal oxide, a metal nitride, a metal carbide, a metal sulfide, or the like. In this specification, "metal" includes metalloids. The ceramic may be, for example, an oxide, a nitride, a carbide, a sulfide, or the like containing at least one element selected from aluminum (Al), zirconium (Zr), titanium (Ti), zinc (Zn), nickel (Ni), iron (Fe), magnesium (Mg), calcium (Ca), and silicon (Si). In addition, when the ink is used to form a conductive fired film, for example, by including non-conductive ceramic powder in the ink, it is possible to impart heat resistance, etc. to the printed layer. In this case, when the entire ceramic powder is taken as 100% by weight, the content ratio of the conductive ceramic powder is, for example, 50% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more, and the remainder is non-conductive ceramic powder.

The shape (outer shape) of the ceramic powder may be spherical or non-spherical. From the viewpoint of easily increasing the packing density of the ceramic powder in the fired film, for example, spherical ceramic powder having an average aspect ratio of 1.2 or less, preferably 1.15 or less, for example 1.1 or less, can be preferably used. Non-spherical shapes include, for example, plate-like, scale-like, flake-like, and amorphous shapes. From the viewpoint of easily increasing the contact area between ceramic particles, for example, non-spherical ceramic powder having an average aspect ratio of more than 1.2, preferably 1.3 or more, 1.5 or more, for example 1.7 or more, and more preferably 2 or more can be used. From the viewpoint of synergizing the above effects, the ceramic powder may be a mixture of spherical particles and non-spherical particles. In this specification, the term "average aspect ratio" refers to the arithmetic average of the aspect ratios (ratio of long diameter to short diameter) based on the long diameter and short diameter of multiple particles (e.g., 10 to 300 particles) randomly selected from the image obtained by observing the ceramic powder with a scanning electron microscope (SEM).

In order to improve the ejection properties of inkjet ink, for example, reducing the viscosity of the ink and increasing the dispersibility of inorganic powder in the ink are sometimes considered. On the other hand, when an ink containing a low-viscosity, well-dispersed ceramic powder is used, the thickness of the center of the printed film becomes smaller than the thickness of the edge, which is called the "coffee ring phenomenon." In addition, for example, if the ink viscosity is increased to reduce the ink flowability so that the ink does not flow toward the outside of the printed film after the printing film is formed, the film thickness of the center of the printed film may locally increase due to surface tension. If the printed film has an uneven thickness, the printed film may shrink due to heat during drying and baking, which may cause cracks in the baked film or peel off the baked film. The present inventor has studied the viscosity and the degree of aggregation of the ceramic powder in the ink for ink containing ceramic powder.

The average primary particle diameter D _P of the ceramic powder may be, for example, 100 nm to 500 nm. From the viewpoint of achieving a suitable ink viscosity by appropriately agglomerating the ceramic powder in the ink, the average primary particle diameter D _P is preferably 475 nm or less, more preferably 450 nm or less, and even more preferably 425 nm or less. On the other hand, from the viewpoint of preventing the ceramic powder from excessively agglomerating in the ink, the average primary particle diameter D _P is preferably 150 nm or more, more preferably 200 nm or more, and even more preferably 250 nm or more.

In this specification, the term "average primary particle diameter D _P " refers to the average primary particle diameter (D ₅₀ ) of the ceramic powder when the ceramic powder dispersed in the dispersion medium is measured by the dynamic light scattering (DLS) method. The average particle diameter based on the DLS method is measured in accordance with JIS Z 8828:2013. The ceramic powder "dispersed in the dispersion medium" means that each ceramic particle exists alone in the dispersion medium, and that there are no aggregates in which two or more ceramic particles are aggregated. In the measurement of the average primary particle diameter D _P , for example, as described in the test example described later, it is preferable to disperse the ceramic powder in the dispersion medium by ultrasonic treatment or the like before measuring. If necessary, a dispersant may be used. Examples of the dispersion medium include isobornyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether acetate, dipropylene glycol monomethyl ether acetate, butyl glycol acetate, butyl diglycol acetate, menthanol propionate, methanol, ethanol, propanol, isopropanol, butanol, n-amyl alcohol, hexanol, heptanol, n-octanol, 2-ethylhexanol, isooctanol, nonanol, decanol, isoundecanol, lauryl alcohol, cetyl alcohol, stearyl alcohol, and water.

The average particle diameter of the ceramic powder in the ink is one factor that allows the ceramic powder to be in a favorable dispersed state in the ink both before and after printing. From the viewpoint of realizing favorable ink viscosity by moderately agglomerating the ceramic powder in the ink and from the viewpoint of suppressing clogging of the ceramic powder at the ejection port of the inkjet device, the average particle diameter in the ink is, for example, 500 nm or less, preferably 475 nm or less, and more preferably 450 nm or less. On the other hand, from the viewpoint of suppressing excessive agglomeration of the ceramic powder in the ink, the average particle diameter in the ink is, for example, 100 nm or more, preferably 150 nm or more, more preferably 200 nm or more, and even more preferably 250 nm or more. The average particle diameter (D ₅₀ ) of the ceramic powder in the ink refers to the average particle diameter of the ceramic powder when the ink is measured by a dynamic scattering method. In the following description, the average particle diameter of the ceramic powder in the ink is also referred to as the "average particle diameter D _I ".

From the viewpoint of appropriately realizing the effects of the technology disclosed herein, it is preferable that the ratio (D _I /D _P ) of the average primary particle diameter D _P to the average particle diameter D _I is 1.05 to 1.5. The average particle diameter D _I being larger than the average primary particle diameter D _P indicates that ceramic particles in an aggregated state are present in the ink. By aggregating the ceramic particles in the ink, the fluidity of the ceramic particles in the ink can be reduced. In addition, by adjusting the balance between the degree of aggregation of the ceramic particles in the ink and the viscosity of the ink, it is possible to suppress local aggregation of the ceramic particles in the printed film. Therefore, it is possible to suppress the occurrence of a difference in the film thickness of the printed film between the part where the ceramic particles are locally aggregated and the other parts. The ratio (D _I /D _P ) is preferably 1.46 or less, more preferably 1.35 or less, and also preferably 1.06 or more.

The content of inorganic powder (e.g., ceramic powder) in the ink is not particularly limited and can be adjusted appropriately depending on the type of fired film (e.g., the electrode to be formed, etc.). For example, as the content of inorganic powder in the ink increases, it becomes easier to form a printed film of suitable thickness with fewer printing runs, and the uniformity of the film thickness in the printed film can be improved. From this perspective, when the entire ink is taken as 100% by weight, the content of ceramic powder is, for example, 1% by weight or more, preferably 3% by weight or more, more preferably 5% by weight or more, and even more preferably 10% by weight or more. On the other hand, if the content of inorganic powder becomes too large, the inorganic powder tends to aggregate too much in the ink, and the uniformity of the film thickness in the printed film tends to decrease. From this perspective, when the entire ink is taken as 100% by weight, the content of ceramic powder is, for example, 50% by weight or less, preferably 40% by weight or less, and more preferably 30% by weight or less.

(B) Binder Resin The binder resin is an organic compound that fixes the inorganic powder on the substrate after the ink is inkjet printed on the substrate. The ink inkjet printed on the substrate is, for example, heated and dried on the substrate, and then baked. Therefore, it is preferable that the binder resin is one that completely disappears (burns out) during the baking process.

The binder resin is not particularly limited, but may be, for example, a resin material that has thermoplasticity and is burned away by a baking process (for example, heating and baking at 200°C or higher). Examples of binder resins include natural polymer compounds such as polyvinyl butyral, carrageenan, and xanthan gum; cellulose-based polymer compounds such as ethyl cellulose and carboxymethyl cellulose; acrylic resins; epoxy resins; phenolic resins; amine resins; and alkyl resins. The amount of binder may be, for example, 0.5% to 10% by weight when the total ink is taken as 100% by weight.

(C) Organic Solvent The organic solvent is not particularly limited. An organic solvent used for this type of application can be appropriately selected and used. Examples of organic solvents include isobornyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether acetate, dipropylene glycol monomethyl ether acetate, butyl glycol acetate, butyl diglycol acetate, menthanol propionate, methanol, ethanol, propanol, isopropanol, butanol, n-amyl alcohol, hexanol, heptanol, n-octanol, 2-ethylhexanol, isooctanol, nonanol, decanol, isoundecanol, lauryl alcohol, cetyl alcohol, stearyl alcohol, water, etc. Mixtures of these solvents may also be used. The blending amount of the solvent is preferably, for example, 50% by weight to 99% by weight when the total weight of the ink is taken as 100% by weight.

(D) Other Additives Additives used in this type of application may be added to the ink as long as they do not impair the effects of the technology disclosed herein. Examples of additives include dispersants (e.g., cationic dispersants), plasticizers, defoamers, release agents, antioxidants, thickeners, pore formers (pore forming materials), etc. The amount of additives to be added may be, for example, 0.1 parts by weight to 10 parts by weight when the total amount of the ink is 100 parts by weight.

<Ink properties>
The ink disclosed herein has a viscosity of 10 (mPa·s) or less. The lower the viscosity of the ink, the less likely the ink will adhere to the nozzle of the inkjet device, and the better the ink ejection properties. From this viewpoint, the viscosity of the ink is preferably 9.5 (mPa·s) or less, and more preferably 9.0 (mPa·s) or less. On the other hand, the higher the viscosity of the ink, the less likely the ejected ink will spread on the substrate, and the less likely the film thickness of the printed film will be uneven. In addition, the higher the viscosity of the ink, the less likely it will scatter from the nozzle of the inkjet device. From this viewpoint, the viscosity of the ink is, for example, 5 (mPa·s) or more, preferably 5.5 (mPa·s) or more, more preferably 6.0 (mPa·s) or more, even more preferably 6.5 (mPa·s) or more, and particularly preferably 7.0 (mPa·s) or more or 7.5 (mPa·s) or more. In this specification, the "viscosity" of the ink is a value measured at a shear rate of 10 (1/s) in an environment of 25° C., as described in the test examples described later. A commercially available viscometer can be used for such measurements.

2. Preparation of Ink Next, the procedure for preparing (manufacturing) the ink disclosed herein will be described. The ink is prepared by mixing the above-mentioned components, followed by crushing and dispersing the inorganic powder. FIG. 1 is a cross-sectional view that shows a schematic diagram of a stirring and grinding machine used in the manufacture of ink. Note that the following description shows an example of a means for preparing the ink disclosed herein, and is not intended to limit the technology disclosed herein.

When manufacturing the ink, first, the above-mentioned components are weighed and mixed to prepare a slurry (including a paste and a suspension) which is a precursor of the ink. At this time, (B) a binder resin and (C) an organic solvent may be mixed to prepare a vehicle in advance. Then, the ink is prepared by stirring the slurry and crushing the inorganic powder using a stirring and crushing machine 100 as shown in FIG. 1. For example, after adding crushing beads (e.g., zirconia beads having an average particle size of 10 μm to 500 μm (e.g., 100 μm to 400 μm)) to the slurry, the slurry is supplied from the supply port 110 into the stirring vessel 120. A shaft 134 having a plurality of stirring blades 132 is housed in the stirring vessel 120. One end of the shaft 134 is attached to a motor (not shown), and the motor is operated to rotate the shaft 134, and the slurry is stirred by the plurality of stirring blades 132 while being sent downstream in the liquid sending direction D. During this stirring, the inorganic powder is crushed by the crushing beads, and the fine inorganic powder is dispersed in the slurry. The slurry sent downstream in the liquid sending direction D passes through the filter 140. As a result, the inorganic powder and the crushing beads that were not atomized are collected in the filter 140, and the ink with the inorganic powder sufficiently dispersed is discharged from the discharge port 150.

The viscosity of the ink and the ratio (D _I /D _P ) can be adjusted by the above-mentioned stirring time. The stirring time is preferably 30 minutes to 10 hours, for example. From the viewpoint of allowing the aggregated ceramic powder to be present in the ink appropriately and from the viewpoint of appropriately adjusting the viscosity of the ink, the stirring time is preferably 30 minutes or more, and more preferably 1 hour or more. On the other hand, if the stirring time is too long, the ceramic powder tends to aggregate too much and the viscosity of the ink tends to increase too much. From this viewpoint, the stirring time is preferably about 5 hours or less, and preferably 4 hours or less. In addition, the viscosity of the ink and the "average particle diameter D _I " can be adjusted to a desired range by adjusting the rotation speed of the shaft 134, the pore size of the filter 140, the average particle diameter and filling rate of the disintegration beads, and the like.

3. Uses of the Ink The ink disclosed herein is used, for example, to form an electrode of an electrochemical cell. In this specification, the term "electrochemical cell" refers to a device capable of converting chemical energy into electrical energy, and a device capable of converting electrical energy into chemical energy, and refers to a device having an anode, a cathode, and an electrolyte. In this specification, the term "anode" refers to an electrode from which electrons flow into an external circuit. In this specification, the term "cathode" refers to an electrode from which electrons flow into from an external circuit. An example of an electrochemical cell is a fuel cell. In a fuel cell, for example, power (electrical energy) can be extracted from chemical energy generated by a combustion reaction between hydrogen and oxygen. Fuel cells include, for example, a solid oxide fuel cell (SOFC) having a solid electrolyte as an electrolyte, and a proton-conducting ceramic fuel cell (PCFC: Protonic Ceramic Fuel Cell). Another example of an electrochemical cell is an electrolysis cell. In an electrolysis cell, for example, a chemical reaction can be caused to generate hydrogen and oxygen from water (e.g., water vapor) by applying electrical energy to the water. The electrolyte includes, for example, a solid oxide electrolysis cell (SOEC) having a solid electrolyte as the electrolyte. The following embodiment will be described by taking as an example a case where the technology disclosed herein is applied to an SOFC.

Figure 2 is a cross-sectional view of an electrochemical cell 200. As shown in Figure 2, the electrochemical cell 200 includes a hydrogen electrode 210, a solid electrolyte layer 220, and a cathode 230. In this embodiment, the electrochemical cell 200 is an SOFC. Here, the hydrogen electrode 210 is the anode, and the cathode 230 is the cathode.

The hydrogen electrode 210 is, for example, an electrode (fuel electrode) to which a fuel gas containing hydrogen is supplied. Examples of the fuel gas include hydrogen gas (H ₂ ); and hydrocarbon gas such as methane (CH ₄ ). The hydrogen electrode 210 preferably has a porous structure so that the fuel gas is appropriately supplied to the inside of the membrane. In the hydrogen electrode 210, for example, oxide ions supplied from the air electrode 240 through the solid electrolyte layer 220 react with the fuel gas to generate electrons. For this reason, the hydrogen electrode 210 uses a mixed membrane in which an inorganic powder (ion conductive powder) having oxide ion conductivity and an inorganic powder (catalyst powder) that promotes the oxidation of the fuel gas are mixed.

The ion conductive powder may be, for example, a ceramic powder used in this type of application. As such ceramic powder, metal oxides such as zirconium oxide and cerium oxide _are preferably used. _The zirconium oxide may include, for example, zirconia and stabilized zirconia. The stabilized zirconia may include zirconia with _Y2O3 , _{Sc2O3 , Yb2O3} , _Gd2O3 , CaO, _MgO , or _CeO2 dissolved therein. The cerium oxide may include, for example, _ceria and doped _ceria . The doped ceria may include ceria with _{Sm2O3 , Gd2O3} , or _Y2O3 dissolved therein. As the catalyst powder, for example, metal powders used in this type of application, such as nickel (Ni), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru), cobalt (Co), lanthanum (La), strontium (Sr), titanium (Ti), etc.; metal oxide powders containing these metal elements; etc., are preferably used. When the entire inorganic powder in the hydrogen electrode 210 is taken as 100% by weight, the content ratio of the ion conductive powder may be set to, for example, 10% by weight to 60% by weight.

The solid electrolyte layer 220 may have, for example, a function of conducting oxide ions. As shown in FIG. 2, the solid electrolyte layer 220 is formed on the upper surface of the hydrogen electrode 210. The solid electrolyte layer 220 may, for example, conduct oxide ions generated at the air electrode 230 to the hydrogen electrode 210. The solid electrolyte layer 220 may also function as a separator that separates the hydrogen electrode 210 and the air electrode 230 from each other. From this perspective, it is preferable that the solid electrolyte layer 220 is a dense layer.

The solid electrolyte layer 220 may be made of a solid electrolyte. The solid electrolyte may be, for example, a ceramic material having oxide ion conductivity. As such a solid electrolyte, any solid electrolyte used for this type of application may be used without particular limitation. For example, oxides containing elements such as zirconium (Zr), cerium (Ce), magnesium (Mg), scandium (Sc), titanium (Ti), aluminum (Al), yttrium (Y), calcium (Ca), gadolinium (Gd), samarium (Sm), barium (Ba), lanthanum (La), strontium (Sr), gallium (Ga), bismuth (Bi), niobium (Nb), and tungsten (W) may be used. Among these, zirconium oxides such as zirconia and stabilized zirconia; and cerium oxides such as ceria and doped ceria; may be preferably used. The solid electrolyte may be made of one or more solid electrolytes. The stabilized zirconia and doped ceria are as described above.

The air electrode 230 is, for example, an electrode to which a gas containing oxygen (e.g., air) is supplied. The air electrode 230 preferably has a porous structure so that oxygen is appropriately supplied to the inside of the membrane. The oxygen supplied to the air electrode 230 is, for example, converted into oxide ions and sent to the hydrogen electrode 210 through the solid electrolyte layer 220. In this embodiment, a fired film formed using the ink disclosed herein is used as the air electrode 230. That is, the air electrode 230 here can be composed of the ceramic powder contained in the ink described above. And, as described above, by using the ink disclosed herein, the uniformity of the film thickness is improved in the air electrode 230. Therefore, in the electrochemical cell 200, which is an SOFC, cracking, peeling, etc. of the air electrode 230 is suppressed, so that the power generation efficiency is maintained at a high level.

The electrochemical cell 200 shown in FIG. 2 is an SOFC having a hydrogen electrode 210, a solid electrolyte layer 220, and an air electrode 230. However, this is not limited to this. The electrochemical cell 200 may have a reaction suppression layer between the solid electrolyte layer 220 and the air electrode 230, as necessary. The reaction suppression layer may be made of a material similar to the reaction suppression layer of a conventionally known SOFC, without any particular restrictions.

(1) Printing Fig. 3 is a schematic overall view of an example of an inkjet device. Fig. 4 is a schematic cross-sectional view of an inkjet head of the inkjet device in Fig. 3. The ink disclosed herein is printed on the surface of a printing target by an inkjet device 1 as shown in Fig. 3. The printing target is, for example, a sintered body W (see Fig. 1) including a hydrogen electrode 210 and a solid electrolyte layer 220 provided on the hydrogen electrode 210. Note that, here, a case will be described in which the ink disclosed herein is used to form an air electrode 230 on a sintered body in which a reaction suppression layer is formed on the surface of the solid electrolyte layer 220 opposite to the surface on which the hydrogen electrode 210 is formed.

First, the structure of the inkjet device 1 shown in Figure 3 will be described. The inkjet device 1 includes an inkjet head 10 that stores ink. The inkjet head 10 is housed inside a print cartridge 40. The print cartridge 40 is inserted into a guide shaft 20 and is configured to reciprocate along the axial direction X of the guide shaft 20. Although not shown, the inkjet device 1 also includes a moving means for moving the guide shaft 20 in the vertical direction Y. This allows the inkjet device 1 to eject ink at a desired position on the fired body W.

For example, a piezoelectric inkjet head as shown in FIG. 4 is used as the inkjet head 10. In this piezoelectric inkjet head 10, a storage section 13 for storing ink is provided in a case 12, and the storage section 13 is connected to a discharge section 16 via a liquid transfer path 15. This discharge section 16 is provided with a discharge port 17 that opens to the outside of the case 12, and a piezoelectric element 18 is arranged to face the discharge port 17. In this inkjet head 10, the piezoelectric element 18 is vibrated to discharge the ink in the discharge section 16 from the discharge port 17 toward the fired body W (see FIG. 3). Here, the ink is discharged onto the reaction suppression layer of the fired body W to form a printed film.

(2) Drying Process Next, the sintered body W with the ink ejected onto the reaction suppression layer is subjected to a drying process in which the sintered body W is heated at a predetermined temperature. This removes the organic solvent from the ink, and a dry film of the air electrode 230 is formed on the sintered body W. The heating temperature in the drying process is preferably set to a temperature (e.g., 50°C to 120°C) at which the organic solvent is removed and at which sintering of the inorganic powder does not occur. The time for the drying process may be, for example, 1 minute to 60 minutes.

(3) Firing Process Next, a firing process is performed for firing the dried film of the air electrode 230 together with the fired body W. As a result, the organic components (e.g., binder resin, additives, etc.) in the ink disappear, and the inorganic powder is sintered to form a fired film (here, the air electrode 230). The firing temperature may be set to a temperature such that the maximum firing temperature is 800° C. to 1200° C., for example. The firing process time may be set to 30 minutes to 8 hours, for example.

In the above embodiment, the ink disclosed herein has been described as an ink used to form the air electrode 230 of the electrochemical cell 200, which is an SOFC. However, this is not limited thereto. The electrochemical cell 200 may be an SOEC. In this case, the electrochemical cell 200, which is an SOEC, has an air electrode 230 with improved film thickness uniformity, thereby improving the oxidation efficiency of oxide ions at the electrode (oxygen gas production efficiency), and ultimately improving the hydrogen gas production efficiency in the electrochemical cell 200.

The technology disclosed herein includes the technologies described in the following sections.
Item 1:
An inkjet ink containing a ceramic powder, a binder resin, and an organic solvent,
wherein an average primary particle diameter of the ceramic powder when the ceramic powder dispersed in a dispersion medium is measured by a dynamic scattering method is defined as D _P , and an average particle diameter of the ceramic powder when the ink-jet ink is measured by the dynamic scattering method is defined as D _I , a ratio of the average primary particle diameter D _P to the average particle diameter D _I (D _I /D _P ) is 1.05 or more and 1.5 or less,
An ink-jet ink having a viscosity of 10 (mPa·s) or less.
Item 2:
2. The ink-jet ink according to item 1, wherein the average primary particle diameter D _P is 100 nm or more and 500 nm or less.
Item 3:
3. The ink-jet ink according to item 1 or 2, wherein the content of the ceramic powder is 5% by weight or more and 40% by weight or less when the entire ink-jet ink is taken as 100% by weight.
Item 4:
4. The ink-jet ink according to any one of items 1 to 3, wherein the ratio (D _I /D _P ) is 1.06 or more and 1.35 or less.
Item 5:
5. The ink-jet ink according to any one of items 1 to 4, wherein the viscosity is 7 (mPa·s) or more and 9 (mPa·s) or less.
Clause 6:
Item 6. The ink-jet ink according to any one of Items 1 to 5, wherein the ceramic powder is a conductive ceramic powder.
Clause 7:
Item 7. The ink-jet ink according to any one of Items 1 to 6, which is used to form an electrode of an electrochemical cell.

Next, test examples related to the technology disclosed herein will be described. Note that the test examples shown below are not intended to limit the technology disclosed herein. Note that "%" and "parts" are by weight unless otherwise specified.

[Example 1]
The ceramic powder _{La0.6Sr0.4Co0.2Fe0.8O3} powder and an ethyl _cellulose vehicle were mixed in a weight ratio of 20:80 _, and a cationic dispersant ("Hypermer KD _{- 1} " manufactured by Croda Japan Co., Ltd.) was added thereto. In this case, the average primary particle diameter _Dp of the ceramic powder was measured. The average primary particle diameter _Dp of the ceramic powder was measured by dispersing the ceramic powder in butyl diglycol acetate as a dispersion medium using a commercially available analyzer ("Zetasizer Nano ZS" manufactured by Malvern Panalytical Co., Ltd.), preparing a sample of a suitable concentration by ultrasonic dispersion, performing DLS measurement at 20 ° C., and calculating based on a general cumulant method. As a result, the average primary particle diameter _Dp was 300 μm. The ethyl cellulose vehicle was prepared by mixing ethyl cellulose (organic binder) and butyl diglycol acetate (organic solvent) in a weight ratio of 1:99, stirring the mixture at 90° C. for 1 hour at 300 rpm using a hot stirrer, and then allowing it to cool naturally. The content of the dispersant was 0.6 parts relative to the total mixture (100 parts) of the ceramic powder, the ethyl cellulose vehicle, and the dispersant.

The mixture of the ceramic powder, ethyl cellulose vehicle, and dispersant, and zirconia beads (particle diameter: 0.3 mm) were placed in a commercially available batch-type bead mill device (Easy Nano RMBII type manufactured by Imex Co., Ltd.) and bead mill processing was performed. Here, 365 parts of zirconia beads were used per total of the above mixture (100 parts). The rotation speed of the device was 1,500 rpm. The filling rate of the zirconia beads in the device was 48 volume %. The processing time was 1 hour. After the bead mill processing, the zirconia beads were separated by pressure filtration using a filter. In this way, the ink according to this example was obtained.

[Examples 2 to 12]
As _the ceramic powder _{, La0.6Sr0.4Co0.2Fe0.8O3} powder having _an average primary particle diameter _{D P} shown in the corresponding column of Table 1 was used. In addition, the processing time in the bead mill processing, the rotation speed in the bead mill processing, and the weight ratio of the organic binder in the ink were appropriately changed so that the average particle diameter D _P of the ceramic powder in the ink and the viscosity of the ink were the desired values. Other than that, the inks according to each example were obtained using the same materials and procedures as in Example 1.

[Calculation of the ratio (D _I /D _P )]
Using the ink of each example as a sample, the average particle diameter _DI was calculated using the above-mentioned analysis device. The ratio ( _DI / _DP ) was calculated from the average primary particle diameter _DP of the ceramic powder and the average particle diameter _DI . The results are shown in the corresponding column in Table 1. Note that the larger the ratio ( _DI / _DP ), the more the ceramic powder is aggregated in the ink. Also, the smaller the ratio ( _DI / _DP ), the more the ceramic powder is dispersed in the ink.

[Viscosity measurement]
The viscosity of the ink in each example was measured. Specifically, the viscosity of the ink in each example was measured using a rotational rheometer ("HAAKE MARS rheometer" manufactured by Thermo Scientific) in an environment of 25°C. During the measurement, the shear rate was changed from 0.1 (1/s) to 1000 (1/s), and the value at a shear rate of 10 (1/s) was extracted. The results are shown in the corresponding columns in Table 1.

[Inkjet printing]
Using an inkjet printer ("Material Printer DMP-2831" manufactured by Fuji Film Corporation), 5 μl of the ink of each example was printed on an area of ^0.2 cm2 on an alumina substrate. After printing, the substrate was heated at 80° C. for 30 minutes. This resulted in a dried film of each example.

[Evaluation of film thickness uniformity]
The thickness of the dry film of each example was measured at any five points using a laser microscope. The thickness difference of the dry film of each example was calculated by subtracting the minimum value from the maximum value of the measured thickness. The results are shown in the corresponding column of Table 1.

Furthermore, based on the above-mentioned film thickness difference, the stability of the film thickness uniformity was evaluated using the following indices. The results are shown in the corresponding columns in Table 1.
"E (Excellent: excellent uniformity)": The film thickness difference was less than 20 μm.
"G (Good: good uniformity)": The film thickness difference was 20 μm or more and less than 25 μm.
"P (Poor: poor uniformity)": The film thickness difference was 25 μm or more.

From the results shown in Table 1, it was found that the dried films of Examples 1 to 6 had better uniformity of film thickness than the dried films of Examples 7 to 12. This shows that a film with a more uniform thickness can be formed by using an ink having a ratio (D _I /D _P ) of 1.05 or more and 1.5 or less and a viscosity of 10 (mPa·s) or less.

The technology disclosed herein has been described above, but these are merely examples and do not limit the scope of the claims. Various modifications may be made to the technology disclosed herein without departing from the spirit of the technology.

Reference Signs List 1 Inkjet device 10 Inkjet head 12 Case 13 Storage section 15 Liquid delivery path 16 Discharge section 17 Discharge port 18 Piezo element 20 Guide shaft 40 Print cartridge 100 Stirring and grinding machine 110 Supply port 120 Stirring container 132 Stirring blade 134 Shaft 140 Filter 150 Discharge port 200 Electrochemical cell 210 Hydrogen electrode 220 Solid electrolyte layer 230 Air electrode

Claims (7)

An inkjet ink containing a ceramic powder, a binder resin, and an organic solvent,
wherein an average primary particle diameter of the ceramic powder when the ceramic powder dispersed in a dispersion medium is measured by a dynamic scattering method is defined as D _P , and an average particle diameter of the ceramic powder when the ink-jet ink is measured by the dynamic scattering method is defined as D _I , a ratio of the average primary particle diameter D _P to the average particle diameter D _I (D _I /D _P ) is 1.05 or more and 1.5 or less,
An ink-jet ink having a viscosity of 10 (mPa·s) or less. The ink-jet ink according to claim 1 , wherein the average primary particle diameter D _P is 100 nm or more and 500 nm or less. The inkjet ink according to claim 1, wherein the content of the ceramic powder is 5% by weight or more and 40% by weight or less when the entire inkjet ink is taken as 100% by weight. The ink-jet ink of claim 1 , wherein the ratio (D _I /D _P ) is 1.06 or greater and 1.35 or less. The inkjet ink according to claim 4, wherein the viscosity is 7 (mPa·s) or more and 9 (mPa·s) or less. The inkjet ink according to any one of claims 1 to 5, wherein the ceramic powder is a conductive ceramic powder. The inkjet ink of claim 6, which is used to form an electrode of an electrochemical cell.

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