Inkjet ink composition

Abstract

Provided is a technique capable of contributing to the improvement in dischargeability of an inkjet ink composition containing a metal-containing nanomaterial and used for forming a layer including a light-emitting element, and to the improvement in dispersibility of the metal-containing nanomaterial in the composition. More specifically, an inkjet ink composition according to an embodiment of the present invention contains: a metal-containing nanomaterial composed of a material selected from the group consisting of a hole injection material, a hole transport material, an electron transport material, and an electrode material; and a dispersion medium containing a glycol-based solvent and a non-glycol-based solvent. Said inkjet ink composition has a bulk modulus of elasticity at 25°C of 2.0 GPa or more and 2.7 GPa or less.

Description

Inkjet ink composition

[0001] The present invention relates to ink-jet ink compositions.

[0002] Layers contained between an anode and a cathode in organic electroluminescent elements and quantum dot light-emitting diodes are sometimes formed by inkjet printing. For example, Patent Document 1 describes forming an electron transport layer by inkjet printing. Patent Document 2 describes forming a hole injection layer, a hole transport layer, and an electron transport layer by inkjet printing.

[0003] JP 2021-116345 A International Publication No. 2022 / 070296

[0004] The present invention aims to provide a technology that contributes to improving the ejection properties of an inkjet ink composition containing a metal-containing nanomaterial used to form a layer containing a light-emitting element, and to improving the dispersibility of the metal-containing nanomaterial in this composition.

[0005] According to one aspect of the present invention, there is provided an inkjet ink composition comprising a metal-containing nanomaterial selected from the group consisting of a hole injection material, a hole transport material, an electron transport material, and an electrode material, and a dispersion medium containing a glycol-based solvent and a non-glycol-based solvent, and having a bulk modulus of elasticity at 25°C of 2.0 GPa or more and 2.7 GPa or less.

[0006] According to another aspect of the present invention, there is provided an inkjet ink composition according to the above aspect, wherein the dispersion medium contains the glycol-based solvent and the non-glycol-based solvent in a blending ratio that satisfies the following formula: 0.05≦R2 / (R1+R2)≦0.50, where R1 represents the content (mass %) of the glycol-based solvent relative to the dispersion medium, and R2 represents the content (mass %) of the non-glycol-based solvent relative to the dispersion medium.

[0007] According to yet another aspect of the present invention, there is provided the ink-jet ink composition according to any one of the above aspects, wherein the glycol-based solvent is one or more selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, triethylene glycol, and hexylene glycol.

[0008]

[0016] According to yet another aspect of the present invention, there is provided the inkjet ink composition according to any one of the above aspects, wherein the non-glycol-based solvent is one or more selected from the group consisting of monoalcohol compounds, amide compounds, aliphatic ester compounds, and aliphatic ether compounds.

[0009] According to yet another aspect of the present invention, there is provided the ink-jet ink composition according to any of the above aspects, wherein the non-glycol-based solvent has a surface tension of 35 mN / m or less at 25°C and a viscosity of 5 mPa s or less at 25°C.

[0010] According to yet another aspect of the present invention, there is provided an inkjet ink composition according to any of the above aspects, wherein the metal-containing nanomaterial comprises one or more of a plurality of types of nanomaterials, each of which contains bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, titanium oxide, indium tin oxide, tin oxide, and silver.

[0011] According to yet another aspect of the present invention, there is provided an inkjet ink composition according to any of the above aspects, wherein the metal-containing nanomaterial includes at least one of a nanomaterial containing nickel oxide, a nanomaterial containing zinc oxide, a nanomaterial containing magnesium-doped zinc oxide, and a nanomaterial containing silver.

[0012] According to yet another aspect of the present invention, there is provided an inkjet ink composition according to any of the above aspects, wherein the metal-containing nanomaterial includes at least one of nanoparticles having an average particle diameter in the range of 1 nm to 100 nm as measured by dynamic light scattering and nanowires having a wire diameter in the range of 1 nm to 100 nm.

[0013] According to yet another aspect of the present invention, there is provided an ink-jet ink composition according to any one of the above aspects, wherein the content of the metal-containing nanomaterial is in the range of 0.01 to 20% by weight.

[0014] According to yet another aspect of the present invention, there is provided an inkjet ink composition according to any of the above aspects, comprising nickel oxide nanoparticles as the metal-containing nanomaterial, ethylene glycol as the glycol-based solvent, and diethylene glycol monomethyl ether as the non-glycol-based solvent.

[0015] According to yet another aspect of the present invention, there is provided an inkjet ink composition according to any of the above aspects, comprising silver nanowires as the metal-containing nanomaterial, ethylene glycol as the glycol-based solvent, and diethylene glycol monomethyl ether as the non-glycol-based solvent.

[0016] According to yet another aspect of the present invention, there is provided a method for manufacturing a display device, comprising: applying an inkjet ink composition according to any of the above aspects to a substrate by an inkjet method to form one or more coating films; and curing the coating films to form one or more functional layers.

[0017] According to yet another aspect of the present invention, there is provided the manufacturing method according to the above aspect, wherein the one or more functional layers include any one of a hole injection layer, a hole transport layer, an electron transport layer, and a light-transmitting electrode layer.

[0018] According to yet another aspect of the present invention, there is provided a display device comprising one or more functional layers each made of a cured product of the ink-jet ink composition according to any of the above aspects.

[0019] According to yet another aspect of the present invention, there is provided a display device according to the above aspect, wherein the one or more functional layers include any one of a hole injection layer, a hole transport layer, an electron transport layer, and a light-transmitting electrode layer.

[0020] According to yet another aspect of the present invention, there is provided a display device according to any of the above aspects, wherein the one or more functional layers include any of a hole injection layer, a hole transport layer, and a light-transmitting electrode layer.

[0021] According to the present invention, a technology is provided that contributes to improving the ejection properties of an inkjet ink composition containing a metal-containing nanomaterial used to form a layer including a light-emitting element, and to improving the dispersibility of the metal-containing nanomaterial in this composition.

[0022] FIG. 1 is a cross-sectional view of a display device according to one embodiment of the present invention.

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments described below are more specific embodiments of any of the above aspects. The following items can be incorporated into each of the above aspects, either singly or in combination.

[0024] Furthermore, the embodiments shown below are merely examples of configurations for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention is not limited by the materials, shapes, structures, etc. of the components described below. Various modifications can be made to the technical idea of ​​the present invention within the technical scope defined by the claims.

[0025] It should be noted that the drawings are schematic, and the relationship between dimensions in one direction and dimensions in another direction, and the relationship between the dimensions of one member and the dimensions of another member, etc. may differ from the actual situation.

[0026] <1> Display Device Fig. 1 is a cross-sectional view of a display device according to one embodiment of the present invention. The display device 1 shown in Fig. 1 employs an active matrix driving method and is capable of displaying color images.

[0027] The display device 1 includes a plurality of pixels arranged in the X and Y directions described below. Each pixel includes a first sub-pixel PXR, a second sub-pixel PXG, and a third sub-pixel PXB. Each of the first sub-pixel PXR, the second sub-pixel PXG, and the third sub-pixel PXB includes a light-emitting element and a pixel circuit. Here, as an example, it is assumed that the semiconductor included in the light-emitting element is inorganic.

[0028] The display device 1 includes a substrate 11, an anode 12, a partition layer 13, a hole injection layer 14, a hole transport layer 15, a light-emitting layer 16, an electron transport layer 17, and a cathode 18. The anode 12, the hole injection layer 14, the hole transport layer 15, the light-emitting layer 16, the electron transport layer 17, and a portion of the cathode 18 facing the anode 12 constitute a light-emitting element.

[0029] 1, the X and Y directions are parallel to the display surface of the display device 1 and intersect with each other. According to one example, the X and Y directions are orthogonal to each other. The Z direction is perpendicular to the X and Y directions, i.e., the thickness direction of the display device 1.

[0030] According to one example, the substrate 11 includes an insulating substrate such as a glass substrate and an array section provided on one of its main surfaces. According to another example, the substrate 11 includes a semiconductor substrate such as a silicon substrate and an array section provided on one of its surface regions. The array section includes pixel circuits and wiring for supplying signals and power to the pixel circuits. The pixel circuits are arranged in the X and Y directions. Each pixel circuit includes a transistor as a drive element and a switch, a capacitor, and wiring for connecting them to each other. The transistor is, for example, a field effect transistor. Here, as an example, the drive element is a p-channel field effect transistor and the switch is an n-channel field effect transistor.

[0031] Here, the anodes 12 are pixel electrodes arranged in the X and Y directions corresponding to the pixel circuits on the substrate 11. Each anode 12 is connected to the drain of a drive element included in the corresponding pixel circuit.

[0032] When the substrate 11 is light-transmitting, the display device 1 may be of a top emission type or a bottom emission type, whereas when the substrate 11 is light-shielding, the display device 1 is of a top emission type.

[0033] When the display device 1 is a bottom-emission type, the anode 12 is a light-transmitting electrode layer. Here, "light-transmitting" means that the average light transmittance in the visible light wavelength range from 400 nm to 800 nm is 80% to 100%. The average light transmittance is the average value of the transmittance per 10 nm. The light-transmitting electrode layer is made of an electrode material. Examples of electrode materials that can be used include transparent conductive metal oxides such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide, and fluorine-doped tin oxide (FTO), as well as elemental metals such as silver. The electrode material may be included in the light-transmitting electrode layer in the form of a nanomaterial. Herein, "nanomaterial" refers to a material having at least one dimension in the range of 1 nm to 100 nm. Examples of nanomaterials include nanoparticles, nanowires, nanorods, nanocubes, nanoplates, and nanofibers. Hereinafter, nanomaterials containing metals are referred to as metal-containing nanomaterials. Furthermore, metal-containing nanomaterials in the form of particles are referred to as metal-containing nanoparticles. In particular, metal oxides in the form of nanoparticles are referred to as metal oxide nanoparticles.

[0034] Here, "nanoparticles" refers to particles having an average particle diameter in the range of 1 nm to 200 nm as measured by dynamic light scattering. The average particle diameter of the metal-containing nanoparticles is preferably in the range of 1 nm to 100 nm, and more preferably in the range of 3 nm to 50 nm.

[0035] "Nanowire" means a wire having a diameter in the range of 1 nm to 100 nm. Preferably, the nanowire has a diameter in the range of 1 nm to 75 nm, and more preferably in the range of 3 nm to 50 nm.

[0036] The length of the nanowires is preferably in the range of 1 μm to 100 μm, more preferably in the range of 5 μm to 50 μm.

[0037] When the display device 1 is a top-emission type, the anode 12 preferably includes a light-reflecting layer. The light-reflecting layer is made of, for example, an elemental metal such as aluminum or silver, or an alloy containing one or more of these. A layer made of a metal such as an elemental metal or an alloy can be formed by, for example, a vacuum deposition method.

[0038] The anode 12 including the light-reflecting layer may further include a light-transmitting layer on the light-reflecting layer. The light-transmitting layer may be made of, for example, any of the materials exemplified as electrode materials. The material constituting the upper surface of the anode 12 preferably has a large work function.

[0039] The partition wall layer 13 is provided on the substrate 11 and the anodes 12. The partition wall layer 13 has through holes at the positions of the anodes 12. Each of these through holes has a shape that tapers from the upper opening to the lower opening. The peripheral edge of each anode 12 is covered with the partition wall layer 13, and the central part is exposed to the internal space of the through hole provided in the partition wall layer 13.

[0040] The partition wall layer 13 is made of an insulating material. According to one example, the partition wall layer 13 is made of an inorganic insulating material. According to another example, the partition wall layer 13 is made of a cured resin.

[0041] The hole injection layer 14 covers the central portion of the anode 12 in the through-hole provided in the partition layer 13. The ionization energy of the hole injection layer 14 is typically larger than the work function of the anode 12.

[0042] The hole injection layer 14 is made of a hole injection material, such as nickel oxide (NiO) or bismuth oxide (BiO). ２ O ３ ), cobalt oxide (CoO), copper oxide (Cu ２ O), molybdenum oxide (MoO ３ The hole injection material made of these metal oxides can be contained in the hole injection layer 14 in the form of metal oxide nanoparticles.

[0043] The metal oxide nanoparticles used as the hole injection material preferably have an average particle size measured by dynamic light scattering in the range of 1 nm to 100 nm, more preferably in the range of 3 nm to 50 nm.

[0044] The thickness of the hole injection layer 14 is preferably in the range of 1 nm to 200 nm, and more preferably in the range of 5 nm to 50 nm.

[0045] The hole transport layer 15 covers the hole injection layer 14 in the through-holes provided in the partition layer 13. Typically, the ionization energy of the hole transport layer 15 is greater than the ionization energy of the hole injection layer 14.

[0046] The hole transport layer 15 is made of a hole transport material. The hole transport material is, for example, bismuth oxide (Bi ２ O ３ ), cobalt oxide (CoO), copper oxide (Cu ２ O), molybdenum oxide (MoO ３ The hole injection material made of these metal oxides may be contained in the hole transport layer 15 in the form of metal oxide nanoparticles. The average particle diameter of these metal oxide nanoparticles, as measured by dynamic light scattering, is preferably within the range described above for the hole injection material.

[0047] The thickness of the hole transport layer 15 is preferably in the range of 1 nm to 200 nm, and more preferably in the range of 10 nm to 50 nm.

[0048] The light-emitting layer 16 covers the hole transport layer 15 in the through-holes provided in the partition layer 13. The light-emitting layer 16 typically has a larger ionization energy than the ionization energy of the hole transport layer 15 and a larger electron affinity than the electron affinity of the hole transport layer 15.

[0049] The light-emitting layer 16 is made of a light-emitting material. The light-emitting layers 16 of the first sub-pixel PXR, the second sub-pixel PXG, and the third sub-pixel PXB contain different light-emitting materials. For example, the light-emitting layer 16 of the first sub-pixel PXR, the second sub-pixel PXG, and the third sub-pixel PXB use a light-emitting material that emits red light, a light-emitting material that emits green light, and a light-emitting material that emits blue light, respectively.

[0050] According to one example, the light-emitting material is a quantum dot, which is a semiconductor particle having, for example, a core-shell structure and a particle size ranging from a few nanometers to about 10 nanometers.

[0051] The core is made of a semiconductor that is responsible for emitting light. The emission spectrum of the quantum dot can be changed by changing the type of semiconductor that makes up the core and the particle diameter of the core.

[0052] The shell is a thin layer epitaxially grown on the surface of the core, having a thickness of 1 to 4 atoms. The shell contributes to improving and stabilizing the luminous efficiency. The shell may have a single-layer structure or a multi-layer structure.

[0053] An example of a quantum dot has a core made of InP, covered with a first shell made of ZnSe, and covered with a second shell made of ZnS. Such quantum dots emit red light when the particle size is large, and green light when the particle size is small.

[0054] Another example of quantum dots is a quantum dot with a core made of ZnSeTe, covered with a first shell made of ZnSe, and covered with a second shell made of ZnS. Such quantum dots emit blue light when their particle size is small.

[0055] The quantum dots may have ligands on the surface of the core-shell particles. The ligands are hydrocarbons with functional groups that contribute to improving durability and preventing aggregation in the dispersion. Note that the ligands may be at least partially lost in the display device 1.

[0056] The thickness of the light-emitting layer 16 is preferably in the range of 1 nm to 200 nm, and more preferably in the range of 10 nm to 50 nm.

[0057] The electron transport layer 17 covers the light-emitting layer 16 in the through-holes provided in the partition layer 13. The electron transport layer 17 typically has a larger ionization energy than that of the light-emitting layer 16 and a larger electron affinity than that of the light-emitting layer 16.

[0058] The electron transport layer 17 is made of an electron transport material. The electron transport material is, for example, a metal oxide such as magnesium-doped zinc oxide (MgZnO), zinc oxide (ZnO), or titanium oxide (TiO). The hole injection material made of these metal oxides may be contained in the electron transport layer 17 in the form of metal oxide nanoparticles. The average particle size of these metal oxide nanoparticles, measured by dynamic light scattering, is preferably within the range described above for the hole injection material.

[0059] The thickness of the electron transport layer 17 is preferably in the range of 1 nm to 200 nm, and more preferably in the range of 10 nm to 50 nm.

[0060] The cathode 18 covers the electron transport layer 17 and the exposed portion of the partition wall layer 13. In this example, the cathode 18 is a common electrode facing the plurality of anodes 12.

[0061] When the display device 1 is a bottom-emission type, the cathode 18 preferably includes a light-reflecting layer. The light-reflecting layer is made of, for example, an elemental metal such as aluminum or silver, or an alloy containing one or more of these. A layer made of a metal such as an elemental metal or an alloy can be formed by, for example, a vacuum deposition method.

[0062] When the display device 1 is a top-emission type, the cathode 18 is a light-transmitting electrode layer. The light-transmitting electrode layer is made of an electrode material. As the electrode material, the same electrode material as that described for the anode 12 can be used.

[0063] The work function of the cathode 18 is typically smaller than the work function of the anode 12 and larger than the electron affinity of the electron transport layer 17. The cathode 18 may include a layer made of a material with a low work function, such as an MgAg alloy or an AlLi alloy, between the light-reflecting layer or the light-transmitting electrode layer and the electron transport layer 17.

[0064] The display device 1 may further include one or more other elements. For example, the display device 1 may further include an electron injection layer such as a LiF layer between the electron transport layer 17 and the cathode 18. The display device 1 may further include a sealing film or a sealing substrate that seals the light-emitting element.

[0065] Furthermore, the display device 1 employs a forward structure for the light-emitting element. The light-emitting element may employ an inverted structure in which the stacking order of the layers included therein is reversed.

[0066] <2> Manufacturing Method of Display Device The display device 1 shown in FIG. 1 can be manufactured, for example, by the following method.

[0067] First, a structure including a substrate 11, an anode 12, and a partition layer 13 is prepared.

[0068] Next, the hole injection layer 14 and the hole transport layer 15 are formed sequentially. Each of the hole injection layer 14 and the hole transport layer 15 can be formed, for example, by an inkjet printing method using an ink composition containing metal oxide nanoparticles and a dispersion medium. Specifically, the hole injection layer 14 can be formed by applying the ink composition described above to the anode 12 by an inkjet method to form a coating film, and then curing this coating film. The hole transport layer 15 can be formed, for example, by applying the ink composition described above to the hole injection layer 14 by an inkjet method to form a coating film, and then curing this coating film.

[0069] Next, the light-emitting layer 16 is formed. As described above, the light-emitting layers 16 of the first sub-pixel PXR, the second sub-pixel PXG, and the third sub-pixel PXB are made of different light-emitting materials. Therefore, the light-emitting layer 16 of the first sub-pixel PXR, the second sub-pixel PXG, and the third sub-pixel PXB are formed separately. Each of these light-emitting layers 16 can be formed by using, for example, a lift-off method.

[0070] Next, the electron transport layer 17 is formed. The electron transport layer 17 can be formed, for example, by an inkjet printing method using an ink composition containing metal oxide nanoparticles and a dispersion medium. Specifically, the electron transport layer 17 can be formed by applying the ink composition to the light-emitting layer 16 by an inkjet method to form a coating film, and then curing the coating film.

[0071] Next, the cathode 18 is formed. The cathode 18 can be formed by vacuum deposition, sputtering, or a combination thereof. Thereafter, the light-emitting element is sealed, if necessary. In this manner, the display device 1 shown in the figure is obtained.

[0072] The anode 12 and the cathode 18 can be formed by the same method as that described for the hole injection layer 14, the hole transport layer 15, and the electron transport layer 17, by changing the composition of the ink composition.

[0073] <3> Inkjet Ink Composition As described above, the anode 12, the hole injection layer 14, the hole transport layer 15, the electron transport layer 17, and the cathode 18 can be formed by inkjet printing. The ink composition used for this inkjet printing, i.e., the inkjet ink composition, preferably has excellent inkjet printability and dispersion stability of the metal-containing nanomaterial.

[0074] One or more of the anode 12, the hole injection layer 14, the hole transport layer 15, the electron transport layer 17, and the cathode 18 are preferably formed using an inkjet ink composition having the composition described below.

[0075] That is, a suitable ink-jet ink composition includes a metal-containing nanomaterial and a dispersion medium including a glycol-based solvent and a non-glycol-based solvent. According to one example, the ink-jet ink composition includes a metal-containing nanomaterial and a dispersion medium including a glycol-based solvent and a non-glycol-based solvent.

[0076] The metal-containing nanomaterial is a material selected from the group consisting of hole injection materials, hole transport materials, electron transport materials, and electrode materials. The metal-containing nanomaterial is a nanomaterial containing a metal such as a metal oxide, an elemental metal, or an alloy. Examples of the metal-containing nanomaterial include those described above for the anode 12, hole injection layer 14, hole transport layer 15, electron transport layer 17, and cathode 18.

[0077] Preferably, the metal-containing nanomaterial comprises one or more of a plurality of nanomaterials each comprising bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, titanium oxide, indium tin oxide, tin oxide, and silver, for example, any of these nanomaterials. In one example, the metal-containing nanomaterial comprises one or more of a plurality of nanomaterials each comprising bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, titanium oxide, indium tin oxide, tin oxide, and silver.

[0078] More preferably, the metal-containing nanomaterial comprises at least one of a nickel oxide-containing nanomaterial, a zinc oxide-containing nanomaterial, a magnesium-doped zinc oxide-containing nanomaterial, and a silver-containing nanomaterial, for example, any one of these nanomaterials. In one example, the metal-containing nanomaterial comprises at least one of a nickel oxide-containing nanomaterial, a zinc oxide-containing nanomaterial, a magnesium-doped zinc oxide-containing nanomaterial, and a silver-containing nanomaterial.

[0079] As described above, the metal-containing nanomaterial may be in the form of nanoparticles or nanowires. For example, the metal-containing nanomaterial may include at least one of nanoparticles having an average particle diameter in the range of 1 nm to 100 nm as measured by dynamic light scattering and nanowires having a wire diameter in the range of 1 nm to 100 nm.

[0080] In one example, the metal-containing nanomaterial comprises one or more of a plurality of nanoparticles each comprising bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, titanium oxide, indium tin oxide, tin oxide, and silver. In another example, the metal-containing nanomaterial comprises silver nanowires. Preferably, the metal-containing nanomaterial comprises at least one of nickel oxide-containing nanoparticles, zinc oxide-containing nanoparticles, magnesium-doped zinc oxide-containing nanoparticles, silver-containing nanoparticles, and silver nanowires.

[0081] The proportion of the metal-containing nanomaterial in the inkjet ink composition is preferably in the range of 0.01% by mass to 20% by mass, more preferably in the range of 0.1% by mass to 10% by mass, and even more preferably in the range of 0.5% by mass to 5% by mass.

[0082] The dispersion medium contains a glycol-based solvent. By including a glycol-based solvent in the dispersion medium, the solvent has excellent dispersibility for metal-containing nanomaterials. The glycol-based solvent is preferably a glycol-based solvent having a hydrogen bond parameter δH of the Hansen solubility parameter (HSP) of 14 or more. A glycol-based solvent having a δH of 14 or more is particularly excellent in dispersion stability of nanoparticles. The dispersion medium contains, as a glycol-based solvent having an HSP δH of 14 or more, for example, one or more selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, triethylene glycol, and hexylene glycol. The upper limit of the hydrogen bond parameter δH of the glycol-based solvent may be, for example, 30 or less.

[0083] Here, the Hansen solubility parameter (HSP) is a solubility parameter introduced by Hildebrand, divided into three components: a dispersion term δD, a polar term δP, and a hydrogen bonding term δH. The dispersion term δD represents the energy due to intermolecular dispersion forces, the polar term δP represents the energy due to intermolecular dipole interactions, and the hydrogen bonding term δH represents the energy due to intermolecular hydrogen bonds.

[0084] The dispersion medium further contains a non-glycol solvent. Examples of the non-glycol solvent include monoalcohol compounds, amide compounds, aliphatic ester compounds, aliphatic ether compounds, and sulfoxide compounds. Preferably, the non-glycol solvent is one or more selected from the group consisting of monoalcohol compounds, amide compounds, aliphatic ester compounds, and aliphatic ether compounds.

[0085] Examples of monoalcohol compounds include ethanol, methanol, 1-isopropanol, 2-isopropanol, butanol, isobutyl alcohol, t-butyl alcohol, 2-ethyl-2-hexanol, 4-methyl-2-pentanol, diethylene glycol monomethyl ether (DEM), dipropylene glycol monomethyl ether (DPM), and 1-methoxy-2-propanol (PGME). Examples of amide compounds include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N,N-diethylformamide (DEF), hexamethylphosphoric triamide (HMPA), and tetramethylurea. Examples of aliphatic ester compounds include 3-methoxybutyl acetate and propylene glycol monomethyl ether acetate (PGMEA or PGMAc). Examples of the aliphatic ether compound include propylene glycol monomethyl ether acetate (PGMEA or PGMAc), tetrahydrofuran (THF), diethylene glycol dimethyl ether, and dipropylene glycol dimethyl ether. Examples of the sulfoxide compound include dimethyl sulfoxide (DMSO). In one embodiment, the dispersion medium contains one or more non-glycol solvents selected from these.

[0086] The monoalcohol compound preferably has an ether bond, such as diethylene glycol monomethyl ether (DEM), dipropylene glycol monomethyl ether (DPM), or 1-methoxy-2-propanol (PGME).

[0087] The aliphatic ether compound is preferably linear, and examples of such aliphatic ether compounds include diethylene glycol dimethyl ether and dipropylene glycol dimethyl ether.

[0088] The non-glycol solvent preferably has a surface tension of 35 mN / m or less at 25°C. The surface tension is preferably 20 mN / m or more. The surface tension is measured using a plate method. The surface tension can be measured using a CBVP-Z type surface tensiometer manufactured by Kyowa Interface Science Co., Ltd.

[0089] Furthermore, the viscosity of the non-glycol-based solvent at 25°C is preferably 5 mPa·s or less. The viscosity is preferably 0.5 mPa·s or more. The viscosity is measured using an E-type viscometer. For example, a TVE-22LT viscometer manufactured by Toki Sangyo Co., Ltd. can be used as the E-type viscometer.

[0090] The blending ratio of the glycol solvent to the non-glycol solvent contained in the dispersion medium preferably satisfies 0.05≦R2 / (R1+R2)≦0.50, more preferably 0.10≦R2 / (R1+R2)≦0.50, and even more preferably 0.15≦R2 / (R1+R2)≦0.30, where R1 represents the content (mass%) of the glycol solvent relative to the dispersion medium, and R2 represents the content (mass%) of the non-glycol solvent relative to the dispersion medium.

[0091] The dispersion medium may further contain a solvent other than a glycol-based solvent and a non-glycol-based solvent, as long as it does not affect the above-mentioned effect, i.e., dispersion stability. However, it is preferable that the dispersion medium does not contain water. If the dispersion medium contains water, it is difficult to achieve high dispersion stability of the metal-containing nanomaterial. The total proportion of the glycol-based solvent and the non-glycol-based solvent in the dispersion medium is preferably in the range of 50% to 100% by mass, more preferably in the range of 65% to 100% by mass, even more preferably in the range of 80% to 100% by mass, and particularly preferably 100% by mass. Preferably, the dispersion medium consists of ethylene glycol and diethylene glycol monomethyl ether.

[0092] The proportion of the dispersion medium in the ink-jet ink composition is preferably in the range of 80% to 99% by mass, and more preferably in the range of 85% to 99% by mass.

[0093] The inkjet ink composition described above has a bulk modulus of 2.0 GPa or more and 2.7 GPa or less at 25° C. The bulk modulus is more preferably 2.2 GPa or more and 2.5 GPa or less. The bulk modulus can be adjusted, for example, by changing the composition of the dispersion medium.

[0094] The bulk modulus is measured using a high-pressure vibration densitometer. Specifically, first, the inkjet ink composition is filled into the densitometer. Then, the pressure and density in the initial state are measured. Next, pressure is applied to the inkjet ink composition, and the density is measured. Then, the isothermal compressibility is calculated based on the pressure and density in the initial state and the pressure and density in the pressurized state. Next, the bulk modulus is obtained by calculating the reciprocal of the isothermal compressibility. Note that the bulk modulus can also be calculated by the product of the square of the sound speed and the density.

[0095] The ink-jet ink composition described above does not contain, for example, a surfactant, and in this case, the above-mentioned substances do not remain in the layer made of the ink-jet ink composition, so that the performance of the light-emitting element is not deteriorated by the residue.

[0096] Specific examples of the composition of the inkjet ink composition are shown below. In one example, the inkjet ink composition comprises nickel oxide nanoparticles, ethylene glycol, and diethylene glycol monomethyl ether. In another example, the inkjet ink composition comprises silver nanowires, ethylene glycol, and diethylene glycol monomethyl ether.

[0097] <4> Effects The dispersion medium of the inkjet ink composition described above contains a glycol-based solvent. The glycol-based solvent can maintain the uniform dispersion state of the metal-containing nanomaterial for a long period of time without causing excessive aggregation. However, inkjet ink compositions containing glycol-based solvents generally have high viscosity and large surface tension, resulting in poor ink ejection properties and making them unsuitable for forming coating films.

[0098] The present inventors have found that ink ejection properties can be improved by using a dispersion medium containing a glycol-based solvent and a non-glycol-based solvent and by setting the bulk modulus at 25°C of the inkjet ink composition within the above-mentioned range.

[0099] The inkjet ink composition described above maintains a uniform dispersion state of the metal-containing nanomaterial for a long period of time and has excellent inkjet printing suitability, such as ejection properties and film-forming properties. Therefore, by using this inkjet ink composition, it is possible to form a layer in which the metal-containing nanomaterial is uniformly dispersed with high productivity. Surprisingly, this effect can be achieved by combining specific dispersion solvents and controlling the bulk modulus of the composition without using a dispersant such as an alcoholamine.

[0100] Therefore, the ink-jet ink composition can contribute to improving the performance of the light-emitting element in the display device described above.

[0101] Tests conducted in connection with the present invention are described below. <1> Preparation of Inkjet Ink Composition <1.1> Example 1 An inkjet ink composition containing a metal-containing nanomaterial and a dispersion medium was prepared. Metal nanoparticles made of nickel (II) oxide and having an average particle size of 30 nm were used as the metal-containing nanomaterial. The average particle size of the metal nanoparticles was measured by the dynamic light scattering method described below. The amount of metal nanoparticles was adjusted so that the proportion of metal nanoparticles in the inkjet ink composition was 1% by mass.

[0102] Ethylene glycol (EG) and diethylene glycol monomethyl ether (DEM) were used as dispersion media. The blending ratio of the two solvents was adjusted to 50% by mass of EG and 50% by mass of DEM. The surface tension and viscosity of DEM at 25°C were 34 mN / m and 3.5 mPa s, respectively.

[0103] <1.2> Example 2 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions: In this example, silver nanowires having a diameter of 25 nm and a length of 10 μm were used instead of nickel (II) oxide nanoparticles having an average particle size of 30 nm; and the blending ratio of the two solvents was adjusted to 70% by mass of EG and 30% by mass of DEM.

[0104] <1.3> Comparative Example 1 An inkjet ink composition similar to that of Example 1 was prepared, except for the following: In this example, water alone was used as the dispersion medium instead of a mixed solvent of ethylene glycol (EG) and diethylene glycol monomethyl ether (DEM).

[0105] <1.4> Comparative Example 2 An inkjet ink composition similar to that of Example 1 was prepared, except for the following points: In this example, zinc oxide nanoparticles having an average particle size of 30 nm were used instead of nickel (II) oxide nanoparticles having an average particle size of 30 nm, and ethanol alone was used as the dispersion medium instead of a mixed solvent of ethylene glycol (EG) and diethylene glycol monomethyl ether (DEM).

[0106] <1.5> Comparative Example 3 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions: In this example, silver nanowires with a diameter of 25 nm and a length of 10 μm were used instead of nickel (II) oxide nanoparticles with an average particle size of 30 nm, and ethylene glycol alone was used as the dispersion medium instead of a mixed solvent of ethylene glycol (EG) and diethylene glycol monomethyl ether (DEM).

[0107] <2> Evaluation <2.1> Dispersion Stability The average particle size of the metal oxide nanoparticles was measured immediately after preparation for each of the inkjet ink compositions according to Example 1 and Comparative Examples 1 and 2. The average particle size was measured by dynamic light scattering. A Nanotrac (registered trademark) UPA-EX150 particle size distribution analyzer manufactured by Nikkiso Co., Ltd. was used to measure the average particle size.

[0108] Furthermore, each of the inkjet ink compositions according to Example 1 and Comparative Examples 1 and 2 was allowed to stand for 720 hours in an environment at 5° C. immediately after preparation. Thereafter, the average particle size of the metal oxide nanoparticles was measured using the same method as above.

[0109] The average particle diameter D immediately after preparation ０ Average particle diameter D after standing for 720 hours ７２０ and average particle diameter D ０ The ratio of the difference between７２０ -D ０ ) / D ０ was calculated as the particle size change rate. Inkjet ink compositions with a particle size change rate of less than 0.10 were evaluated as "A" for dispersion stability. Inkjet ink compositions with a particle size change rate of 0.10 or more were evaluated as "B" for dispersion stability.

[0110] Furthermore, each of the inkjet ink compositions according to Example 2 and Comparative Example 3 was allowed to stand in an environment of 5°C for 720 hours immediately after preparation. Thereafter, it was confirmed whether or not precipitation of silver nanowires occurred. Inkjet ink compositions in which no precipitation occurred were evaluated as "A" in terms of dispersion stability. Inkjet ink compositions in which precipitation occurred were evaluated as "B" in terms of dispersion stability.

[0111] <2.2> Inkjet printability Each of the inkjet ink compositions according to Examples 1 and 2 and Comparative Examples 1 to 3 was filled into an inkjet device and then ejected. The inkjet ink compositions ejected from the inkjet device were evaluated as "A" for inkjet printability. The inkjet ink compositions not ejected from the inkjet device were evaluated as "B" for inkjet printability. An inkjet device equipped with a piezo-type inkjet head was used as the inkjet device.

[0112] <2.3> Measurement of Bulk Modulus The bulk modulus at 25° C. was measured for each of the inkjet ink compositions according to Examples 1 and 2 and Comparative Examples 1 to 3 in accordance with the method described above.

[0113] <2.6> Summary of Evaluation The results of the above evaluation are shown in Table 1 below.

[0114]

[0115] As shown in Table 1, the inkjet ink composition of Comparative Example 1, which used only water as the dispersion medium and had a bulk modulus at 25°C within the above-mentioned range, had excellent inkjet printing suitability but poor dispersion stability of the metal-containing nanomaterial.

[0116] Furthermore, the inkjet ink compositions of Comparative Example 2, which used only ethanol as the dispersion medium and whose bulk modulus at 25°C was not within the above-mentioned range, and Comparative Example 3, which used only ethylene glycol (EG) as the dispersion medium and whose bulk modulus at 25°C was not within the above-mentioned range, had excellent dispersion stability of the metal-containing nanomaterial but poor suitability for inkjet printing.

[0117] In contrast, the inkjet ink compositions of Examples 1 and 2 were excellent in dispersion stability of metal oxide nanoparticles and inkjet printability.

[0118] The HSP [δD, δP, δH] of ethylene glycol used as the glycol solvent in Examples 1 and 2 was [δD = 17, δP = 11, δH = 26], indicating a high δH. Diethylene glycol, propylene glycol, trimethylene glycol, triethylene glycol, and hexylene glycol, which were previously listed along with ethylene glycol as preferred glycol solvents, all have a δH of 14 or greater, indicating a high δH similar to that of ethylene glycol. Furthermore, these glycol solvents are low-molecular-weight alkylene glycols having 6 or less carbon atoms and have a molecular structure similar to that of ethylene glycol. The inventors arbitrarily selected propylene glycol [δD=16.8, δP=10.4, δH=21.3] and trimethylene glycol [δD=16.8, δP=13.5, δH=23.2] from the glycol-based solvents described above, and prepared 1% by mass dispersions of NiO (average particle size: 30 nm) for each of these glycol-based solvents and ethylene glycol, and measured the particle size distribution. As a result, it was confirmed that propylene glycol and trimethylene glycol exhibited the same particle size distribution as ethylene glycol and exhibited the same dispersion stability as ethylene glycol.

[0119] From these, it can be easily inferred that, in Examples 1 and 2, even when any one selected from diethylene glycol, propylene glycol, trimethylene glycol, triethylene glycol, and hexylene glycol is used in place of ethylene glycol, an inkjet ink composition exhibiting the same effects as those of Examples 1 and 2 can be obtained.

[0120] 1...display device, 11...substrate, 12...anode, 13...partition layer, 14...hole injection layer, 15...hole transport layer, 16...light-emitting layer, 17...electron transport layer, 18...cathode, PXB...third sub-pixel, PXG...second sub-pixel, PXR...first sub-pixel.

Claims

1. An inkjet ink composition comprising a metal-containing nanomaterial selected from the group consisting of hole injection materials, hole transport materials, electron transport materials, and electrode materials, and a dispersion medium containing a glycol-based solvent and a non-glycol-based solvent, and having a bulk modulus of elasticity at 25°C of 2.0 GPa or more and 2.7 GPa or less.

2. The inkjet ink composition according to claim 1, wherein the dispersion medium contains the glycol-based solvent and the non-glycol-based solvent in a blending ratio that satisfies the following formula: 0.05≦R2 / (R1+R2)≦0.50, where R1 represents the content (mass %) of the glycol-based solvent relative to the dispersion medium, and R2 represents the content (mass %) of the non-glycol-based solvent relative to the dispersion medium.

3. The ink-jet ink composition according to claim 1 or 2, wherein the glycol-based solvent is one or more selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, triethylene glycol, and hexylene glycol.

4. The ink-jet ink composition according to any one of claims 1 to 3, wherein the non-glycol solvent is one or more selected from the group consisting of monoalcohol compounds, amide compounds, aliphatic ester compounds, and aliphatic ether compounds.

5. The ink-jet ink composition according to any one of claims 1 to 4, wherein the non-glycol solvent has a surface tension of 35 mN / m or less at 25°C and a viscosity of 5 mPa·s or less at 25°C.

6. The ink-jet ink composition according to any one of claims 1 to 5, wherein the metal-containing nanomaterial comprises one or more of a plurality of types of nanomaterials each containing bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, titanium oxide, indium tin oxide, tin oxide, and silver.

7. The ink-jet ink composition according to any one of claims 1 to 6, wherein the metal-containing nanomaterial comprises at least one of a nanomaterial containing nickel oxide, a nanomaterial containing zinc oxide, a nanomaterial containing magnesium-doped zinc oxide, and a nanomaterial containing silver.

8. An inkjet ink composition according to any one of claims 1 to 7, wherein the metal-containing nanomaterial comprises at least one of nanoparticles having an average particle diameter in the range of 1 nm to 100 nm as measured by dynamic light scattering and nanowires having a wire diameter in the range of 1 nm to 100 nm.

9. The ink-jet ink composition according to any one of claims 1 to 8, wherein the content of the metal-containing nanomaterial is in the range of 0.01 to 20% by mass.

10. An ink-jet ink composition according to any one of claims 1 to 9, comprising nickel oxide nanoparticles as the metal-containing nanomaterial, ethylene glycol as the glycol-based solvent, and diethylene glycol monomethyl ether as the non-glycol-based solvent.

11. An inkjet ink composition according to any one of claims 1 to 9, comprising silver nanowires as the metal-containing nanomaterial, ethylene glycol as the glycol-based solvent, and diethylene glycol monomethyl ether as the non-glycol-based solvent.

12. A method for manufacturing a display device, comprising: applying the inkjet ink composition according to any one of claims 1 to 11 to a substrate by an inkjet method to form one or more coating films; and curing the coating films to form one or more functional layers.

13. The manufacturing method according to claim 12, wherein the one or more functional layers include any one of a hole injection layer, a hole transport layer, an electron transport layer, and a light-transmitting electrode layer.

14. A display device comprising one or more functional layers each made of a cured product of the ink-jet ink composition according to any one of claims 1 to 11.

15. The display device according to claim 14, wherein the one or more functional layers include any one of a hole injection layer, a hole transport layer, an electron transport layer, and a light-transmitting electrode layer.

16. The display device according to claim 14, wherein the one or more functional layers include any one of a hole injection layer, a hole transport layer, and a light-transmitting electrode layer.

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