Inkjet ink composition

Abstract

A technology is provided that can contribute to improving the performance of a light-emitting device that has a layer made of metal oxide nanoparticles between a cathode and an anode. The inkjet ink composition includes metal oxide nanoparticles made of a material selected from the group consisting of a hole injection material, a hole transport material, and an electron transport material; a dispersion medium containing a glycol solvent and a non-alcohol solvent having a hydrogen bond term δH of the Hansen solubility parameter of 8 or more; and one of an acidic additive and a basic additive, and when the acidic additive is included, the concentration of the acidic additive is 1×10 -5 mol / L to 1×10 -2 mol / L, and when the basic additive is included, the concentration of the basic additive is 1×10 -5 mol / L to 1×10 -3 mol / L.

Description

[Technical Field]

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

[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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-116345 [Patent Document 2] International Publication No. 2022 / 070296 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a technique that can contribute to improving the performance of a light-emitting device having a layer of metal oxide nanoparticles between a cathode and an anode. [Means for solving the problem]

[0005] According to one aspect of the present invention, there is provided a dispersion medium comprising metal oxide nanoparticles made of a material selected from the group consisting of a hole injection material, a hole transport material, and an electron transport material; a dispersion medium including a glycol-based solvent and a non-alcohol-based solvent having a hydrogen bond term δH of the Hansen solubility parameter of 8 or more; and one of an acidic additive and a basic additive, wherein when the acidic additive is included, the concentration of the acidic additive is 1×10 -5 mol / L to 1×10 -2mol / L, and when the basic additive is included, the concentration of the basic additive is 1×10 -5 mol / L to 1×10 -3 mol / L of an ink-jet ink composition is provided.

[0006] According to another aspect of the present invention, there is provided the inkjet ink composition according to the above aspect, wherein the acidic additive is one or more selected from the group consisting of acetic acid, formic acid, propionic acid, oxalic acid, boric acid, and phosphoric acid.

[0007] According to yet another aspect of the present invention, there is provided an ink-jet ink composition according to the above aspect, wherein the basic additive is one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, magnesium hydroxide, ammonia, pyridine, and triethylamine.

[0008] 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 ΔH of the non-alcoholic solvent is 30 or less.

[0009] According to yet another aspect of the present invention, there is provided the inkjet ink composition according to the above aspect, wherein the dispersion medium contains the glycol-based solvent and the non-alcohol-based solvent in a blending ratio that satisfies the following formula: 0.10≦R2 / (R1+R2)≦0.50 In the formula, R1 represents the total content (mass %) of the glycol-based solvents relative to the dispersion medium, and R2 represents the total content (mass %) of the non-alcohol-based solvents relative to the dispersion medium.

[0010] According to yet another aspect of the present invention, there is provided the inkjet ink composition according to any of the above aspects, wherein the non-alcohol-based solvent is one or more selected from the group consisting of an amide compound, an aliphatic ester compound, and an aliphatic ether compound.

[0011] According to yet another aspect of the present invention, there is provided an ink-jet ink composition according to any of the above aspects, wherein the metal oxide nanoparticles comprise one or more of a plurality of types of nanoparticles, each of which contains bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide.

[0012] According to yet another aspect of the present invention, there is provided an ink-jet ink composition according to any of the above aspects, wherein the metal oxide nanoparticles include at least one of nanoparticles containing nickel oxide, nanoparticles containing zinc oxide, and nanoparticles containing magnesium-doped zinc oxide.

[0013] 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 metal oxide nanoparticles have an average particle size in the range of 3 nm to 50 nm as measured by dynamic light scattering.

[0014] 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 content of the metal oxide nanoparticles is in the range of 0.05 to 20% by mass.

[0015] According to yet another aspect of the present invention, there is provided the inkjet ink composition according to any 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, triethylene glycol, and hexylene glycol.

[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, and an electron transport 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, and an electron transport layer. [Effects of the Invention]

[0020] According to the present invention, a technique is provided that can contribute to improving the performance of a light-emitting device having a layer made of metal oxide nanoparticles between a cathode and an anode. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a cross-sectional view of a display device according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] 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.

[0023] 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.

[0024] 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.

[0025] <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 is a display device that employs an active matrix driving method and is capable of displaying color images.

[0026] The display device 1 includes a plurality of pixels arranged in the X and Y directions (described later). 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, the semiconductor included in the light-emitting element is assumed to be inorganic.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] When the substrate 11 is light-transmitting, the display device 1 may be of a top emission type or a bottom emission type, and when the substrate 11 is light-shielding, the display device 1 is of a top emission type.

[0032] When the display device 1 is a bottom-emission type, the anode 12 is a light-transmitting electrode. Examples of materials that can be used for the light-transmitting electrode include transparent conductive oxides such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide, and fluorine-doped tin oxide (FTO). A layer made of a transparent conductive oxide can be formed by, for example, a sputtering method.

[0033] 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. Layers made of metals such as elemental metals and alloys can be formed by, for example, vacuum deposition.

[0034] 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 for the light-transmitting electrode. The material constituting the upper surface of the anode 12 preferably has a large work function.

[0035] 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 periphery of each anode 12 is covered with the partition wall layer 13, and the center is exposed to the internal space of the through hole provided in the partition wall layer 13.

[0036] 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 insulator. According to another example, the partition wall layer 13 is made of a cured resin.

[0037] 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.

[0038] The hole injection layer 14 is made of a hole injection material. The hole injection material is, for example, a metal oxide such as nickel oxide (NiO), bismuth oxide (BiO), cobalt oxide (CoO), copper oxide (CuO), molybdenum oxide (MoO), or magnesium oxide (MgO). The hole injection material made of these metal oxides may be contained in the hole injection layer 14 in the form of metal oxide nanoparticles.

[0039] 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. Preferably, metal oxide nanoparticles have an average particle diameter in the range of 3 nm to 50 nm as measured by dynamic light scattering.

[0040] 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.

[0041] 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.

[0042] The hole transport layer 15 is made of a hole transport material. Examples of the hole transport material include metal oxides such as bismuth oxide (Bi2O3), cobalt oxide (CoO), copper oxide (Cu2O), molybdenum oxide (MoO3), and magnesium oxide (MgO). 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 size of these metal oxide nanoparticles, measured by dynamic light scattering, is preferably within the range described above for the hole injection material.

[0043] 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.

[0044] 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 hole transport layer 15 and a larger electron affinity than the hole transport layer 15.

[0045] The light-emitting layer 16 is made of a light-emitting material. The light-emitting layers 16 of the first subpixel PXR, the second subpixel PXG, and the third subpixel PXB contain different light-emitting materials. For example, the light-emitting layer 16 of the first subpixel PXR, the second subpixel PXG, and the third subpixel PXB contain a red light-emitting material, a green light-emitting material, and a blue light-emitting material, respectively.

[0046] 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 nm to about 10 nm.

[0047] 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.

[0048] The shell is a thin layer epitaxially grown on the surface of the core, with 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.

[0049] 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.

[0050] Another example of quantum dots is a ZnSeTe core coated with a first shell of ZnSe, which is then coated with a second shell of ZnS. Such quantum dots emit blue light when their particle size is small.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] The cathode 18 covers the electron transport layer 17 and the exposed portion of the partition layer 13. In this example, the cathode 18 is a common electrode facing the plurality of anodes 12.

[0057] 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. Layers made of metals such as elemental metals and alloys can be formed by, for example, vacuum deposition.

[0058] When the display device 1 is a top-emission type, the cathode 18 is a light-transmitting electrode. Examples of materials that can be used for the light-transmitting electrode include transparent conductive oxides such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide, and fluorine-doped tin oxide (FTO). A layer made of a transparent conductive oxide can be formed by, for example, a sputtering method.

[0059] 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 layer made of a metal or a transparent conductive oxide and the electron transport layer 17.

[0060] 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.

[0061] 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.

[0062] <2> Display device manufacturing method The display device 1 shown in FIG. 1 can be manufactured, for example, by the following method.

[0063] First, a structure including a substrate 11, an anode 12, and a partition layer 13 is prepared.

[0064] 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.

[0065] Next, the light-emitting layer 16 is formed. As described above, the light-emitting layers 16 of the first subpixel PXR, the second subpixel PXG, and the third subpixel PXB are different in the light-emitting material contained therein. Therefore, the light-emitting layer 16 of the first subpixel PXR, the light-emitting layer 16 of the second subpixel PXG, and the light-emitting layer 16 of the third subpixel PXB are formed separately. Each of these light-emitting layers 16 can be formed using, for example, a lift-off method.

[0066] 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.

[0067] Next, the cathode 18 is formed. The cathode 18 can be formed by a vacuum deposition method, a sputtering method, or a combination thereof. Thereafter, the light emitting element is sealed as necessary. In this manner, the display device 1 shown in the figure is obtained.

[0068] <3> Inkjet ink composition As described above, the hole injection layer 14, the hole transport layer 15, and the electron transport layer 17 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 metal oxide nanoparticles.

[0069] From this viewpoint, it is preferable that one or more of the hole injection layer 14, the hole transport layer 15, and the electron transport layer 17 are formed using an inkjet ink composition having the composition described below.

[0070] That is, a suitably used ink-jet ink composition includes metal oxide nanoparticles, a dispersion medium including a glycol-based solvent and a non-alcoholic solvent having a hydrogen bond term δH of the Hansen solubility parameter (HSP) of 8 or more, and one of an acidic additive and a basic additive. According to one example, the ink-jet ink composition includes metal oxide nanoparticles, a dispersion medium including a glycol-based solvent and a non-alcoholic solvent having a hydrogen bond term δH of the Hansen solubility parameter (HSP) of 8 or more, and one of an acidic additive and a basic additive.

[0071] The metal oxide nanoparticles are made of a material selected from the group consisting of a hole injection material, a hole transport material, and an electron transport material, and can be any of the metal oxide nanoparticles described above for the hole injection layer 14, the hole transport layer 15, and the electron transport layer 17.

[0072] Preferably, the metal oxide nanoparticles include one or more of a plurality of types of nanoparticles each containing bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide, for example, any of these nanoparticles. More preferably, the metal oxide nanoparticles include at least one of nanoparticles containing nickel oxide, nanoparticles containing zinc oxide, and nanoparticles containing magnesium-doped zinc oxide, for example, any one of these nanoparticles.

[0073] The proportion of metal oxide nanoparticles in the inkjet ink composition is preferably in the range of 0.05% to 20% by mass, more preferably in the range of 0.1% to 10% by mass, and even more preferably in the range of 0.5% to 5% by mass.

[0074] The dispersion medium contains a glycol-based solvent. By containing a glycol-based solvent, the dispersion medium becomes a solvent with excellent dispersibility for metal oxide nanoparticles. The dispersion medium contains, as the glycol-based solvent, one or more selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, and hexylene glycol, for example.

[0075] The dispersion medium further contains a non-alcoholic solvent having a hydrogen bond term ΔH of the Hansen solubility parameter (HSP) of at least 8. By using a non-alcoholic solvent having an HSP ΔH of at least 8 in combination with a glycol-based solvent, inkjet printability is improved without deteriorating dispersibility, and it is possible to achieve both inkjet printability and dispersion stability in the inkjet ink composition.

[0076] Here, the Hansen solubility parameter (HSP) is the solubility parameter introduced by Hildebrand divided into three components: the dispersion term δD, the polar term δP, and the 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.

[0077] Examples of non-alcoholic solvents include aprotic solvents such as amide compounds, aliphatic ester compounds, aliphatic ether compounds, and sulfoxide compounds. The non-alcoholic solvent is preferably one or more compounds selected from the group consisting of amide compounds, aliphatic ester compounds, and aliphatic ether compounds. As described above, the hydrogen bond term δH of the HSP in the non-alcoholic solvent is 8 or more, preferably 10 or more. If the hydrogen bond term δH of the HSP in the non-alcoholic solvent is low, it may be difficult to achieve high dispersibility even if the inkjet printability is improved. The higher the hydrogen bond term δH of the non-alcoholic solvent, the better the dispersibility, which is preferable. Therefore, the upper limit of the hydrogen bond term δH of the non-alcoholic solvent is not particularly limited, but may be, for example, 30 or less.

[0078] Examples of non-alcoholic solvents with an HSP hydrogen bond parameter δH of 8 or greater include N,N-dimethylformamide (DMF) (δH11.3), tetramethylurea (δH11), dimethyl sulfoxide (DMSO) (δH10.2), propylene glycol monomethyl ether acetate (PGMEA or PGMAc) (δH9.8), N,N-dimethylacetamide (DMA) (δH9.4), sulfolane (δH8.7), hexamethylphosphoric triamide (HMPA) (δH8.7), 3-methoxybutyl acetate (δH8.1), and tetrahydrofuran (THF) (δH8.0). In one embodiment, the dispersion medium contains one or more non-alcoholic solvents selected from these.

[0079] The blending ratio of glycol-based solvents to non-alcohol-based solvents contained in the dispersion medium preferably satisfies 0.10≦R2 / (R1+R2)≦0.50, and more preferably 0.15≦R2 / (R1+R2)≦0.30, where R1 represents the total content (mass%) of glycol-based solvents in the dispersion medium, and R2 represents the total content (mass%) of non-alcohol-based solvents in the dispersion medium.

[0080] The dispersion medium may further contain a solvent other than the glycol-based solvent and the non-alcohol-based solvent with a ΔH of 8 or more, 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 oxide nanoparticles. The total proportion of the glycol-based solvent and the non-alcohol-based solvent with a ΔH of 8 or more in the dispersion medium is preferably in the range of 50% by mass to 100% by mass, and more preferably 100% by mass.

[0081] The proportion of the dispersion medium in the inkjet 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.

[0082] The ink-jet ink composition includes one of an acidic additive and a basic additive. When the ink-jet ink composition includes an acidic additive, the concentration of the acidic additive is 1×10 -5 mol / L to 1×10 -2 The concentration of the acidic additive is 1×10 -4 mol / L to 1×10 -3 It is more preferable that the concentration is mol / L.

[0083] The acidic additive is preferably a weak acid. The acidic additive is, for example, an organic acid. The organic acid is, for example, acetic acid, formic acid, propionic acid, or oxalic acid. When an organic acid is used as the acidic additive, the metal contained in the layer made of the inkjet ink composition can be solely derived from the metal oxide nanoparticles.

[0084] The acidic additive may be an inorganic acid, such as phosphoric acid or boric acid.

[0085] The acidic additive is preferably one or more selected from the group consisting of acetic acid, formic acid, propionic acid, oxalic acid, boric acid and phosphoric acid, and more preferably acetic acid.

[0086] When the ink-jet ink composition includes a basic additive, the concentration of the basic additive is 1×10 -5 mol / L to 1×10 -3 mol / L. The concentration of the basic additive is 1×10 -5 mol / L to 1×10 -4 It is more preferable that the concentration is mol / L.

[0087] The basic additive may be, for example, an inorganic base. Examples of the inorganic base include metal hydroxides such as sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, and magnesium hydroxide, as well as ammonia. The basic additive may also be an organic base. Examples of the organic base include pyridine and triethylamine.

[0088] The basic additive is preferably one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, magnesium hydroxide, ammonia, pyridine and triethylamine, and more preferably sodium hydroxide.

[0089] According to one example, the ink-jet ink composition has a surface tension in the range of 20 mN / m to 45 mN / m at 25° C. Preferably, the surface tension of the ink-jet ink composition in the range of 25 mN / m to 35 mN / m at 25° C.

[0090] In addition, the ink-jet ink composition has a viscosity at 25° C. of, for example, 20 mPa·s or less.

[0091] <4> effect The dispersion medium of the inkjet ink composition described above contains a glycol-based solvent. The glycol-based solvent can maintain the metal oxide nanoparticles in a uniformly dispersed state for a long period of time without causing excessive aggregation. However, inkjet ink compositions containing a glycol-based solvent generally have high viscosity and large surface tension, resulting in poor ink ejection properties and making them unsuitable for forming coating films.

[0092] Adding other solvents, such as isopropyl alcohol (IPA) or ethyl acetate (AcOEt), to a glycol-based solvent-containing dispersion medium to adjust the viscosity and surface tension reduces the viscosity and surface tension, but also decreases the dispersion stability of metal oxide nanoparticles.

[0093] An inkjet ink composition containing a glycol-based solvent and a non-alcohol-based solvent with a Hansen solubility parameter (HSP) hydrogen bond term δH of 8 or greater as a dispersion medium does not have an excessively high viscosity or an excessively high surface tension, despite the inclusion of a glycol-based solvent. Therefore, inkjet ink compositions containing these solvents maintain a uniformly dispersed state of metal oxide nanoparticles for a long period of time and exhibit excellent inkjet printing suitability, such as ejection properties and film-forming properties. Therefore, the use of this inkjet ink composition makes it possible to form a layer in which metal oxide nanoparticles are uniformly dispersed with high productivity.

[0094] The present inventors have found that when an inkjet ink composition containing metal oxide nanoparticles and a dispersion medium containing a glycol-based solvent and a non-alcoholic solvent having a hydrogen bonding term δH of the Hansen solubility parameter (HSP) of 8 or more is stored in a high-temperature environment, for example, an environment of 30°C to 50°C, the dispersion stability of the metal oxide nanoparticles decreases. In particular, the present inventors have found that when the inkjet ink composition is stored in a high-temperature environment for a long period of time, for example, 40 to 168 hours, the dispersion stability of the metal oxide nanoparticles decreases. When a hole injection layer, hole transport layer, and electron transport layer are formed using an inkjet ink composition containing metal oxide nanoparticles with reduced dispersion stability, for example, aggregated metal oxide nanoparticles, the performance of these layers may decrease, and therefore the performance of the light-emitting device may also decrease.

[0095] The present inventors have solved the above problem by adding an acidic additive or a basic additive at a concentration within the above-mentioned range to an inkjet ink composition containing metal oxide nanoparticles and a dispersion medium including a glycol-based solvent and a non-alcohol-based solvent having a hydrogen bonding term ΔH of the Hansen solubility parameter (HSP) of 8 or more.

[0096] Therefore, the ink-jet ink composition can contribute to improving the performance of a light-emitting device having a layer of metal oxide nanoparticles between a cathode and an anode. [Example]

[0097] The following describes tests carried out in connection with the present invention. <1> Preparation of Ink-Jet Ink Compositions <1.1> Example 1 An inkjet ink composition was prepared containing metal oxide nanoparticles, a carrier medium, and an acidic additive. The metal oxide nanoparticles used were nickel (II) oxide nanoparticles with an average particle size of 30 nm. The average particle size of the metal oxide nanoparticles was measured by the dynamic light scattering method described below. The amount of the metal oxide nanoparticles was adjusted so that the ratio of the metal oxide nanoparticles to the inkjet ink composition was 1% by mass.

[0098] The dispersion media used were ethylene glycol (EG), N,N-dimethylformamide (DMF), and propylene glycol monomethyl ether acetate (PGMAc). The blending ratio of the three solvents was adjusted to EG 71.43% by mass, DMF 8.93% by mass, and PGMAc 13.39% by mass.

[0099] Acetic acid was used as the acidic additive. Acetic acid was added to the dispersion medium in the form of a 1% by mass acetic acid solution. A solvent having the same composition as the dispersion medium was used as the solvent for the acetic acid solution. The amount of the acetic acid solution was adjusted so that the ratio of the acetic acid solution to the inkjet ink composition was 5.24% by mass. In other words, the molar concentration of acetic acid in the inkjet ink composition was 1×10 -2 The concentration was adjusted to mol / L.

[0100] <1.2> Example 2 An inkjet ink composition similar to that of Example 1 was prepared, except for the following points. That is, in this example, the blending ratio of the three solvents was adjusted to EG 75.01 mass %, DMF 9.38 mass %, and PGMAc 14.06 mass %. The amount of acetic acid solution was adjusted so that the proportion of the acetic acid solution in the inkjet ink composition was 0.55 mass %. That is, the molar concentration of acetic acid in the inkjet ink composition was 1 x 10 -3 The concentration was adjusted to mol / L.

[0101] <1.3> Example 3 An inkjet ink composition similar to that of Example 1 was prepared, except for the following points. That is, in this example, the blending ratio of the three solvents was adjusted to EG 75.01% by mass, DMF 9.38% by mass, and PGMAc 14.07% by mass. A 0.01% by mass acetic acid solution was used as the acetic acid solution. The amount of the acetic acid solution was adjusted so that the proportion of the acetic acid solution in the inkjet ink composition was 0.54% by mass. That is, the molar concentration of acetic acid in the inkjet ink composition was 1×10 -5 The concentration was adjusted to mol / L.

[0102] <1.4> Example 4 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions. That is, in this example, the blending ratio of the three solvents was adjusted to 75.15% by mass of EG, 9.39% by mass of DMF, and 14.09% by mass of PGMAc. Sodium hydroxide was used as a basic additive instead of an acidic additive. Sodium hydroxide was added to the dispersion medium in the form of a 1% by mass sodium hydroxide solution. A solvent having the same composition as the dispersion medium was used as the solvent for the sodium hydroxide solution. The amount of sodium hydroxide solution was adjusted so that the proportion of the sodium hydroxide solution in the inkjet ink composition was 0.37% by mass. That is, the molar concentration of sodium hydroxide in the inkjet ink composition was 1×10 -3 The concentration was adjusted to mol / L.

[0103] <1.5> Example 5 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions. Specifically, in this example, the blending ratio of the three solvents was adjusted to 75.15% by mass of EG, 9.39% by mass of DMF, and 14.09% by mass of PGMAc. Instead of an acidic additive, sodium hydroxide was used as a basic additive. Sodium hydroxide was added to the dispersion medium in the form of a 0.01% by mass sodium hydroxide solution. A solvent having the same composition as the dispersion medium was used as the solvent for the sodium hydroxide solution. The amount of sodium hydroxide solution was adjusted so that the ratio of the sodium hydroxide solution in the inkjet ink composition was 0.37% by mass. Specifically, the molar concentration of sodium hydroxide in the inkjet ink composition was 1×10 -5 The concentration was adjusted to mol / L.

[0104] <1.6> Comparative Example 1 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions: In this example, the blending ratio of the three solvents was adjusted to 75.43% by mass of EG, 9.43% by mass of DMF, and 14.14% by mass of PGMAc, and no acidic additive was used.

[0105] <1.7> Comparative Example 2 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions. That is, in this example, the blending ratio of the three solvents was adjusted to EG 75.01% by mass, DMF 9.38% by mass, and PGMAc 14.06% by mass. Then, 100% by mass of acetic acid was used instead of the acetic acid solution. The amount of acetic acid was adjusted so that the proportion of acetic acid in the inkjet ink composition was 0.55% by mass. That is, the molar concentration of acetic acid in the inkjet ink composition was 1×10 -1 The concentration was adjusted to mol / L.

[0106] <1.8> Comparative Example 3 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions. That is, in this example, the blending ratio of the three solvents was adjusted to 72.72 mass% EG, 9.09 mass% DMF, and 13.64 mass% PGMAc. Sodium hydroxide was used as a basic additive instead of an acidic additive. Sodium hydroxide was added to the dispersion medium in the form of a 10 mass% sodium hydroxide solution. A solvent having the same composition as the dispersion medium was used as the solvent for the sodium hydroxide solution. The amount of sodium hydroxide solution was adjusted so that the proportion of the sodium hydroxide solution in the inkjet ink composition was 3.55 mass%. That is, the molar concentration of sodium hydroxide in the inkjet ink composition was 1 x 10 -1 The concentration was adjusted to mol / L.

[0107] <1.9> Comparative Example 4 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions. Specifically, in this example, the blending ratio of the three solvents was adjusted to 72.72% by mass of EG, 9.09% by mass of DMF, and 13.64% by mass of PGMAc. Sodium hydroxide was used as a basic additive instead of an acidic additive. Sodium hydroxide was added to the dispersion medium in the form of a 1% by mass sodium hydroxide solution. A solvent having the same composition as the dispersion medium was used as the solvent for the sodium hydroxide solution. The amount of sodium hydroxide solution was adjusted so that the proportion of the sodium hydroxide solution in the inkjet ink composition was 3.55% by mass. Specifically, the molar concentration of sodium hydroxide in the inkjet ink composition was 1×10 -2 The concentration was adjusted to mol / L.

[0108] <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 Examples 1 to 5 and Comparative Examples 1 to 4. 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.

[0109] Furthermore, each of the inkjet ink compositions according to Examples 1 to 5 and Comparative Examples 1 to 4 was allowed to stand for 168 hours in an environment at 40° C. immediately after preparation, after which the average particle size of the metal oxide nanoparticles was measured using the same method as above.

[0110] The average particle diameter D after standing for 168 hours was compared with the average particle diameter D immediately after preparation. 168 and the average particle diameter D0 (D 168 The particle size change rate was calculated as (-D0) / D0). 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.

[0111] Furthermore, when the inkjet ink compositions were visually inspected after standing for 168 hours, those inkjet ink compositions for which no change in appearance, such as precipitation, was confirmed were rated as "A" for appearance change, while those inkjet ink compositions for which the above-mentioned change in appearance was confirmed were rated as "B" for appearance change.

[0112] <2.2> Inkjet printability <2.2.1> Measurement of surface tension The surface tension at 25° C. was measured for each of the inkjet ink compositions according to Examples 1 to 5 and Comparative Examples 1 to 4. A CBVP-Z type surface tensiometer manufactured by Kyowa Interface Science Co., Ltd. was used for this measurement.

[0113] <2.2.2> Viscosity measurement The viscosity at 25° C. was measured for each of the inkjet ink compositions according to Examples 1 to 5 and Comparative Examples 1 to 4. A TVE-22LT viscometer manufactured by Toki Sangyo Co., Ltd. was used for this measurement.

[0114] <2.2.3> Evaluation of inkjet printability Inkjet ink compositions having a viscosity at 25°C of 20 mPa·s or less and a surface tension of 20 mN / m to 40 mN / m were rated "A" for inkjet printability.

[0115] The other inkjet ink compositions were rated "B" for inkjet printability.

[0116] <2.3> Summary of evaluation The results of the above evaluations are shown in Table 1 below.

[0117] [Table 1]

[0118] As shown in Table 1, the inkjet ink composition according to Comparative Example 1, which contained neither an acidic nor a basic additive, exhibited poor dispersion stability of metal oxide nanoparticles.

[0119] Furthermore, the inkjet ink compositions according to Comparative Examples 2 to 4, which contained an acidic or basic additive but whose concentration was outside the above-mentioned range, exhibited poor dispersion stability of the metal oxide nanoparticles. Furthermore, the inkjet ink composition according to Comparative Example 3 also showed a change in appearance after being left standing for 168 hours.

[0120] In contrast, the inkjet ink compositions according to Examples 1 to 5 exhibited excellent dispersion stability of the metal oxide nanoparticles. [Explanation of symbols]

[0121] 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. metal oxide nanoparticles made of a material selected from the group consisting of hole injection materials, hole transport materials, and electron transport materials; a dispersion medium containing a glycol solvent and a non-alcohol solvent having a hydrogen bond term δH of the Hansen solubility parameter of 8 or more; One of an acidic additive and a basic additive Including, When the acidic additive is included, the concentration of the acidic additive is 1×10 －５ mol / L to 1×10 －2 mol / L, When the basic additive is included, the concentration of the basic additive is 1×10 －５ mol / L to 1×10 －３ mol / L.

2. 2. The ink-jet ink composition according to claim 1, wherein the acidic additive is at least one selected from the group consisting of acetic acid, formic acid, propionic acid, oxalic acid, boric acid, and phosphoric acid.

3. 2. The ink-jet ink composition according to claim 1, wherein the basic additive is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, magnesium hydroxide, ammonia, pyridine, and triethylamine.

4. 2. The ink-jet ink composition of claim 1, wherein the δH of the non-alcoholic solvent is 30 or less.

5. The ink-jet ink composition according to claim 4 , wherein the dispersion medium contains the glycol-based solvent and the non-alcohol-based solvent in a blending ratio that satisfies the following formula: 0.10≦R2 / (R1+R2)≦0.50 In the formula, R1 represents the total content (mass%) of the glycol-based solvents relative to the dispersion medium, and R2 represents the total content (mass%) of the non-alcohol-based solvents relative to the dispersion medium.

6. 5. The ink-jet ink composition according to claim 4, wherein the non-alcoholic solvent is at least one selected from the group consisting of an amide compound, an aliphatic ester compound, and an aliphatic ether compound.

7. 2. The ink-jet ink composition of claim 1, wherein the metal oxide nanoparticles comprise one or more of a plurality of types of nanoparticles, each of which contains bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide.

8. 2. The ink-jet ink composition of claim 1, wherein the metal oxide nanoparticles comprise at least one of nickel oxide-containing nanoparticles, zinc oxide-containing nanoparticles, and magnesium-doped zinc oxide-containing nanoparticles.

9. 2. The ink-jet ink composition according to claim 1, wherein the metal oxide nanoparticles have an average particle size measured by a dynamic light scattering method in the range of 3 nm to 50 nm.

10. The ink-jet ink composition according to claim 1, wherein the content of the metal oxide nanoparticles is in the range of 0.05 to 20% by mass.

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

12. applying the ink-jet ink composition according to claim 1 to a substrate by an ink-jet method to form one or more coating films; curing the coating to form one or more functional layers; A method for manufacturing a display device comprising the steps of:

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

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

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, and an electron transport layer.

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