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. [Solution] The inkjet ink composition comprises 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-based solvent, and a surface conditioner that disappears upon heat treatment at 200°C for 10 minutes.

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 an inkjet ink composition 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 containing a glycol-based solvent, and a surface conditioner that disappears upon heat treatment at 200°C for 10 minutes.

[0006] According to another aspect of the present invention, there is provided the ink-jet ink composition according to the above aspect, wherein the surface conditioner is an acetylene alcohol-based surface conditioner.

[0007] According to yet another aspect of the present invention, there is provided an ink-jet ink composition according to any of the above aspects, which contains the surface conditioner at a concentration in the range of 1% by mass to 10% by mass.

[0008] 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, molybdenum oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide.

[0009] 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 and nanoparticles containing zinc oxide.

[0010] 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.

[0011] 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.

[0012] According to yet another aspect of the present invention, there is provided a method for manufacturing a display device, comprising: applying the inkjet ink composition according to any of the above aspects to a substrate by inkjet printing to form a coating film; and subjecting the coating film to a heat treatment to remove the surface conditioner from the coating film.

[0013] According to yet another aspect of the present invention, there is provided the manufacturing method according to the above aspect, wherein the heat treatment of the coating film is a heat treatment at 200° C. or higher for 10 minutes or longer.

[0014] According to yet another aspect of the present invention, there is provided a display device comprising one or more layers each made of a cured product of the ink-jet ink composition according to any of the above aspects.

[0015] 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 layers include any one of a hole injection layer, a hole transport layer, and an electron transport layer. [Effects of the Invention]

[0016] 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]

[0017] [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

[0018] 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.

[0019] 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.

[0020] 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.

[0021] <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.

[0022] 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, the semiconductor included in the light-emitting element is assumed to be inorganic.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] Here, "nanoparticles" refers to particles having an average particle diameter in the range of 200 nm to 1 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.

[0036] 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.

[0037] 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.

[0038] 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 (BiO), cobalt oxide (CoO), copper oxide (CuO), molybdenum oxide (MoO), 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 diameter of these metal oxide nanoparticles, measured by dynamic light scattering, is preferably within the range described above for the hole injection material.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The electron transport layer 17 is made of an electron transport material. Examples of the electron transport material include metal oxides such as magnesium-doped zinc oxide (MgZnO), zinc oxide (ZnO), and 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] <2> Display device manufacturing method The display device 1 shown in FIG. 1 can be manufactured, for example, by the following method.

[0059] First, a structure including a substrate 11, an anode 12, and a partition layer 13 is prepared.

[0060] Next, the hole injection layer 14 and the hole transport layer 15 are formed in this order. Each of the hole injection layer 14 and the hole transport layer 15 can be formed by, for example, an inkjet printing method using an ink composition containing metal oxide nanoparticles and a dispersion medium.

[0061] 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.

[0062] Subsequently, 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.

[0063] 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.

[0064] <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.

[0065] Furthermore, if the ink-jet ink composition contains an additive, and if this additive remains in the light-emitting element, the light-emitting element will not achieve the expected light-emitting characteristics. Therefore, it is preferable that the ink-jet ink composition does not contain any additive that may remain in the light-emitting element.

[0066] From these viewpoints, 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.

[0067] That is, a suitably used inkjet ink composition contains metal oxide nanoparticles, a dispersion medium containing a glycol-based solvent, and a surface conditioner that disappears upon heat treatment at 200° C. for 10 minutes. This inkjet ink composition preferably does not contain any other components.

[0068] 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.

[0069] 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, molybdenum oxide, nickel oxide, 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 and nanoparticles containing zinc oxide, for example, any one of these nanoparticles.

[0070] The proportion of metal oxide nanoparticles in the inkjet ink composition is preferably in the range of 0.1% to 10% by mass, and more preferably in the range of 0.5% to 5% by mass.

[0071] The dispersion medium contains a glycol-based solvent, which is, for example, one or more selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, and hexylene glycol.

[0072] The dispersion medium may further contain other solvents. The proportion of glycol solvents in the dispersion medium is preferably in the range of 50% to 100% by mass, and more preferably in the range of 80% to 100% by mass.

[0073] The other solvent is preferably one or more aprotic solvents such as amide compounds, aliphatic ester compounds, and aliphatic ether compounds. The one or more aprotic solvents may include, for example, one or more of N,N'-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and propylene glycol monomethyl ether acetate (PGMEA or PGMAc). The proportion of the aprotic solvent in the other solvents is preferably in the range of 80% to 100% by mass, and more preferably 100% by mass.

[0074] 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.

[0075] The surface conditioner, which disappears upon heat treatment at 200°C for 10 minutes, is a substance that adjusts the surface tension of the ink-jet ink composition. Ink-jet printing is performed, for example, at a temperature within the range of 15°C to 40°C. This surface conditioner is stable in the ink-jet ink composition within this temperature range. The coating film formed from the ink-jet ink composition is baked at a temperature high enough to volatilize the dispersion medium. This surface conditioner disappears from the coating film during this heat treatment.

[0076] The surface conditioner is preferably an acetylene alcohol-based surface conditioner. As the acetylene alcohol-based surface conditioner, it is preferable to use one or more compounds having the following structure:

[0077] The compound used as the acetylene alcohol-based surface conditioner preferably has 5 to 15 carbon atoms, more preferably 6 to 15. Compounds with fewer carbon atoms tend to have poorer ability to reduce the surface tension of the ink-jet ink composition. When a compound with more carbon atoms is used, heating at a higher temperature or for a longer period of time tends to be required to remove the carbon atoms.

[0078] One example of a compound preferred as an acetylene alcohol-based surface conditioner is a compound in which a hydrogen atom is bonded to one of the two carbon atoms forming the acetylene bond, and a carbon atom is bonded to the other of the two carbon atoms forming the acetylene bond, with one hydroxyl group and two alkyl groups bonded to this carbon atom. Another example of a compound preferred as an acetylene alcohol-based surface conditioner is a compound in which a carbon atom is bonded to each of the two carbon atoms forming the acetylene bond, with one hydroxyl group and two alkyl groups bonded to each of these carbon atoms. In these compounds, the number of carbon atoms in the alkyl group is preferably in the range of 1 to 4.

[0079] As such an acetylene alcohol-based surface conditioner, for example, one or more of 2-methyl-3-butyn-2-ol shown in the following formula (1), 3,5-dimethyl-1-hexyn-3-ol shown in the following formula (2), and 2,4,7,9-tetramethyl-5-decyne-4,7-diol shown in the following formula (3) can be used.

[0080] [ka]

[0081] [ka]

[0082] [ka]

[0083] The inkjet ink composition preferably contains a surface conditioner at a concentration in the range of 1% to 10% by mass, and more preferably at a concentration in the range of 2.5% to 5.5% by mass.

[0084] According to one example, the surface tension of the ink-jet ink composition at 25° C. is in the range of 20 mN / m to 40 mN / m. Preferably, the surface tension of the ink-jet ink composition at 25° C. is in the range of 25 mN / m to 35 mN / m.

[0085] In addition, the ink-jet ink composition has a viscosity at 25° C. of, for example, 20 mPa·s or less.

[0086] The dispersion medium of this inkjet ink composition contains a glycol-based solvent. The glycol-based solvent can maintain the uniform dispersion state of the metal oxide nanoparticles for a long period of time without causing excessive aggregation. However, inkjet ink compositions containing glycol-based solvents generally have high surface tension and are therefore unsuitable for forming coating films.

[0087] The addition of a silicone-based surface modifier to an ink-jet ink composition containing a glycol-based solvent reduces the surface tension. However, the surface modifier remains in the coating film formed from such an ink-jet ink composition even after baking. This residue causes a decrease in the performance of the light-emitting device.

[0088] The inkjet ink composition described above, which contains a surface conditioner that disappears upon heat treatment at 200°C for 10 minutes, does not have an excessively high surface tension despite containing a glycol-based solvent. Therefore, this inkjet ink composition maintains a uniformly dispersed state of metal oxide nanoparticles for a long period of time and exhibits 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 metal oxide nanoparticles are uniformly dispersed with high productivity.

[0089] The surface conditioner disappears upon heat treatment at 200°C for 10 minutes. According to one example, heat treatment at 200°C for 10 minutes causes the surface conditioner to thermally decompose and the decomposition products to volatilize. Therefore, the surface conditioner and its decomposition products do not remain in the baked coating film, i.e., in the layer made of the cured product of the inkjet ink composition. Therefore, when the above-mentioned inkjet ink composition is used, degradation of the performance of the light-emitting element due to the residue does not occur.

[0090] In this way, the inkjet 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]

[0091] The following describes tests carried out in connection with the present invention.

[0092] <1> Preparation of Ink-Jet Ink Compositions <1.1> Example 1 An inkjet ink composition was prepared containing metal oxide nanoparticles, a dispersion medium, and additives.

[0093] The metal oxide nanoparticles used were nickel (II) oxide nanoparticles, and the amount of the metal oxide nanoparticles was adjusted so that the ratio of the metal oxide nanoparticles to the inkjet ink composition was 1.00% by mass.

[0094] Ethylene glycol (EG) and N,N'-dimethylformamide (DMF) were used as dispersion media. The amount of ethylene glycol added was 77.50% by mass based on the total amount of the inkjet ink composition. The amount of N,N'-dimethylformamide added was 15.50% by mass based on the total amount of the inkjet ink composition.

[0095] The additive used was Olfine (registered trademark) D-10E manufactured by Nissin Chemical Industry Co., Ltd. This additive is an ethylene glycol solution containing 2,4,7,9-tetramethyl-5-decyne-4,7-diol represented by the following formula (3) at a concentration of 50% by mass. The amount of the additive added was 6.00% by mass based on the total amount of the inkjet ink composition.

[0096] [ka]

[0097] <1.2> Example 2 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions: In this example, the amount of ethylene glycol added was 71.20% by mass, based on the total amount of the inkjet ink composition; the amount of N,N'-dimethylformamide added was 17.80% by mass, based on the total amount of the inkjet ink composition; and the amount of additives added was 10.00% by mass, based on the total amount of the inkjet ink composition.

[0098] <1.3> Example 3 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions: In this example, the amount of ethylene glycol added was 76.80% by mass, based on the total amount of the inkjet ink composition; the amount of N,N'-dimethylformamide added was 19.20% by mass, based on the total amount of the inkjet ink composition; and the amount of additives added was 3.00% by mass, based on the total amount of the inkjet ink composition.

[0099] <1.4> Example 4 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions: In this example, the amount of ethylene glycol added was 79.11% by mass, based on the total amount of the inkjet ink composition; and the amount of N,N'-dimethylformamide added was 9.89% by mass, based on the total amount of the inkjet ink composition. Furthermore, instead of using Olfine (registered trademark) D-10E, manufactured by Nissin Chemical Industry Co., Ltd., SURFYNOL (registered trademark) 61, manufactured by Evonik Operations GmbH, was used as the additive. This additive is a solvent-free liquid consisting of 3,5-dimethyl-1-hexyn-3-ol, as shown in formula (2) below. The amount of the additive added was 10.00% by mass, based on the total amount of the inkjet ink composition.

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[0101] <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 amount of ethylene glycol added was 79.11% by mass, based on the total amount of the inkjet ink composition. Furthermore, the amount of N,N'-dimethylformamide added was 9.89% by mass, based on the total amount of the inkjet ink composition. Furthermore, instead of using Olfine (registered trademark) D-10E manufactured by Nissin Chemical Industry Co., Ltd., Olfine (registered trademark) B manufactured by Nissin Chemical Industry Co., Ltd. was used as the additive. This additive is a solvent-free liquid consisting of 2-methyl-3-butyn-2-ol, as shown in the following formula (1). The amount of the additive added was 10.00% by mass, based on the total amount of the inkjet ink composition.

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[0103] <1.6> Comparative Example 1 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions. Specifically, in this example, ethylene glycol (EG), N,N'-dimethylformamide (DMF), and propylene glycol monomethyl ether acetate (PGMAc) were used as the dispersion media. The amount of ethylene glycol added, based on the total amount of the inkjet ink composition, was 75.43 mass%. The amount of N,N'-dimethylformamide added, based on the total amount of the inkjet ink composition, was 9.43 mass%. The amount of propylene glycol monomethyl ether acetate added, based on the total amount of the inkjet ink composition, was 14.14 mass%. Furthermore, no additives were used in this example.

[0104] <1.7> Comparative Example 2 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions. Specifically, in this example, the amount of ethylene glycol added was 88.20% by mass, based on the total amount of the inkjet ink composition. Furthermore, the amount of N,N'-dimethylformamide added was 9.80% by mass, based on the total amount of the inkjet ink composition. Instead of using Olfine (registered trademark) D-10E, manufactured by Nissin Chemical Industry Co., Ltd., as an additive, a diluted solution prepared by diluting BYK (registered trademark) 378, manufactured by BYK, with ethylene glycol to a concentration of 0.1% by mass was used. BYK (registered trademark) 378, manufactured by BYK, is a solvent-free liquid containing a silicone-based surface conditioner. The amount of additive added, based on the total amount of the inkjet ink composition, was 1.00% by mass.

[0105] <1.8> Comparative Example 3 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions: In this example, the amount of ethylene glycol added was 86.40% by mass, based on the total amount of the inkjet ink composition; and the amount of N,N'-dimethylformamide added was 9.80% by mass, based on the total amount of the inkjet ink composition. Instead of using Olfine (registered trademark) D-10E manufactured by Nissin Chemical Industry Co., Ltd., Olfine (registered trademark) E1004 manufactured by Nissin Chemical Industry Co., Ltd. was used as the additive. This additive is a solvent-free liquid consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate, as shown in formula (4) below (n1 + n2 = 4). The amount of the additive added was 3.00% by mass, based on the total amount of the inkjet ink composition.

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[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 Examples 1 to 5 and Comparative Examples 1 to 3. The average particle size was measured by dynamic light scattering. The average particle size was measured using a Nanotrac (registered trademark) UPA-EX150 particle size distribution analyzer manufactured by Nikkiso Co., Ltd.

[0108] Immediately after preparation, each of the inkjet ink compositions according to Examples 1 to 5 and Comparative Examples 1 to 3 was allowed to stand for 720 hours in an environment at 25° C. After that, the average particle size of the metal oxide nanoparticles was measured using the same method as above.

[0109] The average particle diameter D after standing for 720 hours is compared to the average particle diameter D immediately after preparation. 720 and the average particle diameter D0 (D 720The 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.

[0110] <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 3. A CBVP-Z type surface tensiometer manufactured by Kyowa Interface Science Co., Ltd. was used for this measurement.

[0111] <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 3. A TVE-22LT viscometer manufactured by Toki Sangyo Co., Ltd. was used for the measurement.

[0112] <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 25 mN / m to 35 mN / m were rated "AA" for inkjet printability.

[0113] Inkjet ink compositions that did not satisfy the above conditions but had a viscosity at 25°C of 20 mPa·s or less and a surface tension in the range of 20 mN / m to 40 mN / m were evaluated as "A" for inkjet printability.

[0114] The other inkjet ink compositions were rated "B" for inkjet printability.

[0115] <2.3> Thermal dissipation of additives 0.15 g of each of the additives used in Examples 1 to 5 and Comparative Examples 2 and 3 was weighed into an aluminum cup. Next, each of these aluminum cups was placed on a hot plate heated to 200°C and heated for 10 minutes. Additives whose mass before and after heating differed by less than 0.01 g were evaluated as "A" for thermal dissipation. Additives whose mass before and after heating differed by 0.01 g or more were evaluated as "B" for thermal dissipation.

[0116] <2.4> 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 was excellent in inkjet printing suitability, but was poor in dispersion stability of the metal oxide nanoparticles.

[0119] The inkjet ink compositions of Comparative Examples 2 and 3 were excellent in dispersion stability of metal oxide nanoparticles and inkjet printability, but the additives used in these compositions were not eliminated by heating at 200°C for 10 minutes.

[0120] In contrast, the inkjet ink compositions of Examples 1 to 5 were excellent in dispersion stability of metal oxide nanoparticles and inkjet printability. The inkjet ink compositions of Examples 1 and 2 were particularly excellent in inkjet printability. Furthermore, the additives used in the inkjet ink compositions of Examples 1 to 5 disappeared when heated at 200°C for 10 minutes. [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-based solvent; A surface conditioner that disappears upon heat treatment at 200°C for 10 minutes. An inkjet ink composition comprising:

2. The ink-jet ink composition according to claim 1 , wherein the surface conditioner is an acetylene alcohol-based surface conditioner.

3. The ink-jet ink composition according to claim 1, wherein the surface conditioner is contained in a concentration ranging from 1% by mass to 10% by mass.

4. 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, molybdenum oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide.

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

6. 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.

7. 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.

8. applying the ink-jet ink composition according to claim 1 to a substrate by an ink-jet printing method to form a coating film; subjecting the coating film to a heat treatment to remove the surface conditioner from the coating film; A method for manufacturing a display device comprising the steps of:

9. The method according to claim 8, wherein the heat treatment of the coating film is a heat treatment at 200°C or higher for 10 minutes or longer.

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

11. The display device according to claim 10 , wherein the one or more layers include any one of a hole injection layer, a hole transport layer, and an electron transport layer.

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