Inkjet ink composition

Abstract

Provided is a technology capable of inhibiting the occurrence of defects that accompany formation of a layer composed of metal oxide nanoparticles, which an optical element has between a cathode and an anode, by an inkjet printing method. This inkjet ink composition comprises: metal oxide nanoparticles composed of a material selected from the group consisting of a hole injection material, a hole transport material, and an electron transport material; and a dispersion medium containing a glycol-based solvent and a non-alcohol-based solvent having 7-9 carbon atoms.

Description

Inkjet ink composition

[0001] This disclosure relates to an inkjet ink composition.

[0002] The layers contained between the anode and cathode in organic electroluminescent elements and quantum dot light-emitting diodes can be formed by inkjet printing. For example, Patent Document 1 describes forming an electron transport layer by inkjet printing. Furthermore, Patent Document 1 describes forming a hole injection layer, a hole transport layer, and an electron transport layer by inkjet printing.

[0003] Japanese Patent Publication No. 2021-116345, International Publication No. 2022 / 070296

[0004] The present disclosure aims to provide a technology that can reduce the likelihood of problems occurring when forming a layer of metal oxide nanoparticles between the cathode and anode of a light-emitting element using an inkjet printing method.

[0005] According to one aspect of the present invention, an inkjet ink composition is provided which comprises metal oxide nanoparticles made of a material selected from the group consisting of hole injection materials, hole transport materials, and electron transport materials, and a dispersion medium containing a glycol-based solvent and a non-alcohol-based solvent having 7 to 9 carbon atoms.

[0006] According to another aspect of the present invention, an inkjet ink composition is provided in which the proportion of the non-alcoholic solvent to the total of the glycol-based solvent and the non-alcoholic solvent is in the range of 5% to 35% by mass.

[0007] According to yet another aspect of the present invention, an inkjet ink composition according to any of the above aspects is provided, wherein the non-alcoholic solvent comprises one or more selected from the group consisting of 3-methoxybutyl acetate, diethylene glycol methyl ethyl ether, propylene glycol diacetate, dipropylene glycol dimethyl ether, and dipropylene glycol methyl ether acetate.

[0008] According to yet another aspect of the present invention, an inkjet ink composition according to any of the above aspects is provided, 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.

[0009] According to yet another aspect of the present invention, an inkjet ink composition according to any of the above aspects is provided, comprising the metal oxide nanoparticles in a concentration ranging from 0.05% by mass to 20% by mass.

[0010] According to yet another aspect of the present invention, an inkjet ink composition according to any of the above aspects is provided, comprising one or more nanoparticles of a plurality of types, each containing bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide.

[0011] According to yet another aspect of the present invention, an inkjet ink composition according to any of the above aspects is provided, wherein the metal oxide nanoparticles comprise one or more nanoparticles containing nickel oxide, nanoparticles containing zinc oxide, and nanoparticles containing magnesium-doped zinc oxide.

[0012] According to yet another aspect of the present invention, an inkjet ink composition relating to any of the above aspects is provided, 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.

[0013] According to yet another aspect of the present invention, an inkjet ink composition is provided relating to any of the above aspects, wherein the ratio of the mass of the non-alcoholic solvent to the total mass of the glycol-based solvent and the non-alcoholic solvent is in the range of 5% to 35% by mass, the non-alcoholic solvent comprises one or more selected from the group consisting of 3-methoxybutyl acetate, diethylene glycol methyl ethyl ether, propylene glycol diacetate, dipropylene glycol dimethyl ether, and dipropylene glycol methyl ether acetate, and the metal oxide nanoparticles are contained in a concentration in the range of 0.05% to 20% by mass, and the average particle size of the metal oxide nanoparticles measured by dynamic light scattering is in the range of 3 nm to 50 nm.

[0014] According to yet another aspect of the present invention, a method for manufacturing a display device is provided, which includes applying an inkjet ink composition according to any of the above aspects to a substrate by an inkjet printing method to form a coating film, and curing the coating film to form a functional layer.

[0015] According to yet another aspect of the present invention, a manufacturing method relating to the above aspect is provided, wherein the functional layer is one of a hole injection layer, a hole transport layer, and an electron transport layer.

[0016] According to yet another aspect of the present invention, a display device is provided which comprises one or more layers, each made from a cured product of an inkjet ink composition according to any of the above aspects.

[0017] According to yet another aspect of the present invention, a display device according to the above aspect is provided, wherein the one or more layers include any one of a hole injection layer, a hole transport layer, and an electron transport layer.

[0018] This disclosure provides a technology that can reduce the likelihood of problems occurring when forming a layer of metal oxide nanoparticles between the cathode and anode of a light-emitting element using an inkjet printing method.

[0019] Figure 1 is a cross-sectional view of a display device according to one embodiment of the present invention.

[0020] Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are more specific to any of the above aspects. The matters described below can be incorporated into each of the above aspects, individually or in combination.

[0021] Furthermore, the embodiments shown below illustrate configurations for realizing the technical concept of the present invention, and the technical concept of the present invention is not limited by the material, shape, and structure of the components described below. Various modifications can be made to the technical concept of the present invention within the technical scope defined by the claims described in the claims.

[0022] Please note that the drawings are schematic, and the relationships between dimensions in one direction and those in another, as well as the relationships between the dimensions of one component and those of other components, may differ from those in reality.

[0023] <1> Display Device Figure 1 is a cross-sectional view of a display device according to one embodiment of the present invention. The display device 1 shown in Figure 1 employs an active matrix drive method and is a display device capable of displaying color images.

[0024] The display device 1 includes a plurality of pixels arranged in the X and Y directions, as described later. Each pixel includes a first subpixel PXR, a second subpixel PXG, and a third subpixel PXB. Each of the first subpixel PXR, the second subpixel PXG, and the third subpixel 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 an inorganic material.

[0025] 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 the portion of the cathode 18 facing the anode 12 constitute a light-emitting element.

[0026] In Figure 1, the X and Y directions are parallel to the display surface of the display device 1 and intersect each other. For 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.

[0027] In one example, the substrate 11 includes an insulating substrate such as a glass substrate and an array portion provided on one of its main surfaces. In another example, the substrate 11 includes a semiconductor substrate such as a silicon substrate and an array portion provided on one of its surface regions. The array portion includes pixel circuits and wiring that supplies signals and power to the pixel circuits. The pixel circuits are arranged in the X and Y directions. Each pixel circuit includes transistors and capacitors as driving elements and switches, and wiring that connects them to each other. The transistors are, for example, field-effect transistors. Here, as an example, the driving element is a p-channel field-effect transistor and the switch is an n-channel field-effect transistor.

[0028] The anode 12 in this case is a pixel electrode arranged on the substrate 11 in the X and Y directions, corresponding to the pixel circuit. Each anode 12 is connected to the drain of the driving element included in the corresponding pixel circuit.

[0029] If the substrate 11 is light-transmitting, the display device 1 may be a top-emission type or a bottom-emission type. If the substrate 11 is light-shielding, the display device 1 shall be a top-emission type.

[0030] When the display device 1 is of the bottom emission type, the anode 12 is a light-transmitting electrode. As the material for the light-transmitting electrode, transparent conductive oxides such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide, and fluorine-doped tin oxide (FTO) can be used. The layer made of the transparent conductive oxide can be formed by, for example, a sputtering method.

[0031] When the display device 1 is a top emission type, the anode 12 preferably includes a light reflection layer. The light reflection layer is made of, for example, a single metal such as aluminum and silver or an alloy containing one or more of them. A layer made of a metal such as a single metal and an alloy can be formed by, for example, a vacuum evaporation method.

[0032] The anode 12 including the light reflection layer can further include a light transmission layer on the light reflection layer. As the material of the light transmission layer, for example, those exemplified as the material of the light transmissive electrode can be used. Note that the material constituting the upper surface of the anode 12 preferably has a large work function.

[0033] The partition layer 13 is provided on the substrate 11 and the anode 12. The partition layer 13 has through holes at the positions of the anodes 12. Each of these through holes has a tapered shape from the upper opening toward the lower opening. Each of the anodes 12 is covered with the peripheral portion by the partition layer 13, and the central portion is exposed in the internal space of the through holes provided in the partition layer 13.

[0034] The partition layer 13 is made of an insulator. According to one example, the partition layer 13 is made of an inorganic insulator. According to another example, the partition layer 13 is made of a cured resin.

[0035] The hole injection layer 14 covers the central portion of the anode 12 in the through holes 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.

[0036] The hole injection layer 14 is made of a hole injection material. The hole injection material is, for example, metal oxides such as nickel oxide (NiO), bismuth oxide (Bi ２ O ３ ), cobalt oxide (CoO), copper oxide (Cu ２ O), molybdenum oxide (MoO ３ ), and magnesium oxide (MgO). The hole injection material made of these metal oxides can be included in the hole injection layer 14 in the form of metal oxide nanoparticles.

[0037] Here, "nanoparticles" refers to particles whose average particle diameter, as measured by dynamic light scattering, is in the range of 1 nm to 200 nm. For metal oxide nanoparticles, it is preferable that the average particle diameter, as measured by dynamic light scattering, is in the range of 3 nm to 50 nm.

[0038] 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.

[0039] The hole transport layer 15 covers the hole injection layer 14 within through-holes provided in the partition layer 13. Typically, the ionization energy of the hole transport layer 15 is greater than that of the hole injection layer 14.

[0040] 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 These are metal oxides such as ), and magnesium oxide (MgO). The hole injection material made of these metal oxides may be included in the hole transport layer 15 in the form of metal oxide nanoparticles. It is preferable that the average particle size of these metal oxide nanoparticles, as measured by dynamic light scattering, is within the range described above for the hole injection material.

[0041] 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.

[0042] The light-emitting layer 16 covers the hole transport layer 15 within through holes provided in the partition layer 13. Typically, the light-emitting layer 16 has a higher ionization energy and electron affinity compared to the hole transport layer 15.

[0043] The light-emitting layer 16 is made of a light-emitting material. The first subpixel PXR, the second subpixel PXG, and the third subpixel PXB have different light-emitting materials in their light-emitting layers 16. For example, 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 use a red-emitting material, a green-emitting material, and a blue-emitting material, respectively.

[0044] The light-emitting material is, for example, a quantum dot. A quantum dot is a semiconductor particle that has, for example, a core-shell structure and a particle size in the range of a few nanometers to about 10 nanometers.

[0045] The core consists of a semiconductor responsible for light emission. The emission spectrum of a quantum dot changes by changing the type of semiconductor that makes up the core and the particle size of the core.

[0046] The shell is a thin layer epitaxially grown on the surface of the core, having a thickness of one to four atoms. The shell contributes to improving and stabilizing the luminescence efficiency. The shell may have a single-layer structure or a multi-layer structure.

[0047] One example of a quantum dot is a structure in which a core made of InP is covered with a first shell made of ZnSe, and this is then 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.

[0048] Another example of a quantum dot has a structure in which a core made of ZnSeTe is covered with a first shell made of ZnSe, and this is then covered with a second shell made of ZnS. Such quantum dots emit blue light when the particle size is small.

[0049] Quantum dots may have ligands on the surface of their core-shell particles. The ligands are hydrocarbons with functional groups that contribute to improved resistance and prevention of aggregation in dispersions. However, the ligands may be at least partially absent in the display device 1.

[0050] 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.

[0051] The electron transport layer 17 covers the light-emitting layer 16 within through-holes provided in the partition layer 13. Typically, the electron transport layer 17 has a higher ionization energy and electron affinity compared to the light-emitting layer 16.

[0052] 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), and titanium oxide (TiO). The hole injection material made of these metal oxides may be included in the electron transport layer 17 in the form of metal oxide nanoparticles. It is preferable that the average particle size of these metal oxide nanoparticles, as measured by dynamic light scattering, is within the range described above for the hole injection material.

[0053] 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.

[0054] The cathode 18 covers the electron transport layer 17 and the exposed portion of the partition layer 13. In this case, the cathode 18 is a common electrode facing multiple anodes 12.

[0055] When the display device 1 is of the bottom emission type, it is preferable that the cathode 18 includes a light-reflecting layer. The light-reflecting layer is made of, for example, elemental metals such as aluminum and silver, or an alloy containing one or more of them. Layers made of elemental metals and alloys can be formed, for example, by vacuum deposition.

[0056] When the display device 1 is of the top-emission type, the cathode 18 is a light-transmitting electrode. As the material for the light-transmitting electrode, transparent conductive oxides such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide, and fluorine-doped tin oxide (FTO) can be used. The layer made of the transparent conductive oxide can be formed by, for example, a sputtering method.

[0057] The work function of the cathode 18 is typically smaller than that of the anode 12 and larger than that of 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 transparent conductive oxide and the electron transport layer 17.

[0058] 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 also further include a sealing film or sealing substrate that seals the light-emitting element.

[0059] Furthermore, the display device 1 employs a forward structure for the light-emitting element. The light-emitting element may also employ an inverse structure in which the stacking order of the layers it contains is reversed.

[0060] <2> Method of manufacturing the display device The display device 1 shown in Figure 1 can be manufactured, for example, by the following method.

[0061] First, a structure including a substrate 11, an anode 12, and a partition layer 13 is prepared.

[0062] Next, a hole injection layer 14 and a 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, first, the inkjet ink composition is supplied to the surface of the substrate by an inkjet printing method to form a coating film. Next, this coating film is dried. For example, the coating film is baked. This yields a layer made of cured inkjet ink composition as the printed layer.

[0063] Next, the light-emitting layer 16 is formed. As described above, the first subpixel PXR, the second subpixel PXG, and the third subpixel PXB have different light-emitting materials in their light-emitting layer 16. 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, for example, using the lift-off method.

[0064] 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, similar to how the hole injection layer 14 and hole transport layer 15 were formed.

[0065] Next, the cathode 18 is formed. The cathode 18 can be formed by vacuum deposition, sputtering, or a combination thereof. After that, the light-emitting element is sealed as necessary. In this way, the display device 1 shown in the figure is obtained.

[0066] <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 an inkjet printing method. The ink composition used for this inkjet printing, i.e., the inkjet ink composition, is preferably such that it is less prone to problems associated with forming layers made of metal oxide nanoparticles by an inkjet printing method, for example, it is excellent in inkjet printability and dispersion stability of metal oxide nanoparticles, and is less prone to clogging of the nozzles of the inkjet head.

[0067] From this viewpoint, it is preferable that one or more of the hole injection layer 14, hole transport layer 15, and electron transport layer 17 be formed using an inkjet ink composition having the composition described below. That is, a suitably used inkjet ink composition comprises metal oxide nanoparticles and a dispersion medium containing a glycol-based solvent and a non-alcohol-based solvent having 7 to 9 carbon atoms. This inkjet ink composition preferably does not contain other components that may remain in the light-emitting element. For example, the inkjet ink composition comprises metal oxide nanoparticles and the above-mentioned dispersion medium, and does not contain other components. Preferably, the above-mentioned dispersion medium consists of a glycol-based solvent and a non-alcohol-based solvent having 7 to 9 carbon atoms.

[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. As the metal oxide nanoparticles, those described above with respect to the hole injection layer 14, the hole transport layer 15, and the electron transport layer 17 can be used.

[0069] Preferably, the metal oxide nanoparticles contain 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 contain one or more of nanoparticles containing nickel oxide, nanoparticles containing zinc oxide, and nanoparticles containing magnesium-doped zinc oxide, for example, any of these nanoparticles.

[0070] The proportion of the metal oxide nanoparticles in the inkjet ink composition, that is, the concentration of the metal oxide nanoparticles in the inkjet ink composition, is preferably within the range of 0.05% by mass to 20% by mass, more preferably within the range of 0.1% by mass to 10% by mass, and still more preferably within the range of 0.5% by mass to 5% by mass.

[0071] The inkjet ink composition contains a glycol-based solvent as part of the dispersion medium. The glycol-based solvent has two hydroxy groups in the molecule and a large hydrogen bonding term δ of the Hansen solubility parameter (HSP), which can contribute to the dispersion stability of the metal oxide nanoparticles. The glycol-based solvent is, for example, one or more selected from the group consisting of ethylene glycol (δ Ｈ = 26), diethylene glycol (δ Ｈ = 19), propylene glycol (δ Ｈ = 21.3), triethylene glycol (δ Ｈ = 18.6), and hexylene glycol (δ Ｈ = 15). The glycol-based solvent preferably contains ethylene glycol, and more preferably is ethylene glycol. Ｈ = 15). The glycol-based solvent preferably contains ethylene glycol, and more preferably is ethylene glycol.

[0072] The inkjet ink composition contains, as part of the dispersion medium, a non-alcoholic solvent having 7 to 9 carbon atoms per molecule (hereinafter, unless otherwise specified, "non-alcoholic solvent" refers to a non-alcoholic solvent having 7 to 9 carbon atoms per molecule). The non-alcoholic solvent can contribute to inkjet printability and suppress drying of the inkjet ink composition, i.e., suppression of clogging of the inkjet head nozzles.

[0073] The non-alcoholic solvent is, for example, an aprotic solvent, preferably one or more selected from the group consisting of amide compounds, aliphatic ester compounds, and aliphatic ether compounds. The non-alcoholic solvent may include, for example, one or more selected from the group consisting of 3-methoxybutyl acetate (MBA), diethylene glycol methyl ethyl ether (DMEE), propylene glycol diacetate (PDGA), dipropylene glycol dimethyl ether (DMM), and dipropylene glycol methyl ether acetate (DPMA).

[0074] Non-alcoholic solvents have a surface tension at 25°C that, for example, is in the range of 20 mN / m to 32.5 mN / m. Furthermore, non-alcoholic solvents have a viscosity at 25°C that, for example, is in the range of 0.5 mPa·s to 3 mPa·s.

[0075] Mass M of glycol-based solvent Ａ and the mass M of the non-alcoholic solvent Ｂ The mass M of the non-alcoholic solvent as a percentage of the total Ｂ Percentage M Ｂ / (M Ａ +M Ｂ The amount of ) is preferably in the range of 5% to 35% by mass, more preferably in the range of 7.5% to 25% by mass, and even more preferably in the range of 10% to 20% by mass. Ｂ / (M Ａ +M Ｂ Increasing the ratio of M reduces the viscosity and surface tension of the inkjet ink composition, and also makes it less likely for the inkjet ink composition to dry undesirably. Ｂ / (MＡ +M Ｂ Reducing the ) improves the dispersion stability of the metal oxide nanoparticles The proportion of the dispersion medium in the inkjet ink composition is preferably in the range of 80% to 99.95% by mass, more preferably in the range of 90% to 99.9% by mass, and even more preferably in the range of 95% to 99.5% by mass.

[0076] The inkjet ink composition has a surface tension at 25°C that is, for example, in the range of 20 mN / m to 45 mN / m. Preferably, the surface tension of the inkjet ink composition at 25°C is in the range of 25 mN / m to 35 mN / m.

[0077] Furthermore, the viscosity of the inkjet ink composition at 25°C is, for example, in the range of 1 mPa·s to 20 mPa·s. Preferably, the viscosity of the inkjet ink composition at 25°C is in the range of 5 mPa·s to 14 mPa·s.

[0078] The above inkjet ink composition can be manufactured, for example, by first preparing a dispersion medium containing a glycol-based solvent and a non-alcohol-based solvent, and then dispersing metal oxide nanoparticles in this dispersion medium. Alternatively, the above inkjet ink composition can also be manufactured by first dispersing metal oxide nanoparticles in a glycol-based solvent, and then mixing this dispersion with a non-alcohol-based solvent.

[0079] The dispersion medium of this inkjet ink composition contains a glycol-based solvent. Although metal oxide nanoparticles tend to aggregate in dispersions, the glycol-based solvent can maintain a uniform dispersion state for a long period of time without causing excessive aggregation of metal oxide nanoparticles. An inkjet ink composition with excellent dispersion state and dispersion stability of metal oxide nanoparticles is useful in reducing variations in shape and size during the formation of printed layers.

[0080] However, inkjet ink compositions containing only glycol-based solvents as dispersion media generally have high viscosity and high surface tension. Such inkjet ink compositions have poor ink ejection properties and are unsuitable for forming coating films.

[0081] The viscosity and surface tension of an inkjet ink composition containing a glycol-based solvent can be reduced, for example, by adding a low-viscosity organic solvent. However, the inventors have found that when an inkjet ink composition comprising metal oxide nanoparticles dispersed as dispersion particles in a glycol-based solvent is combined with a low-viscosity organic solvent such as dipropylene glycol methyl-n-propyl ether or dipropylene glycol methyl-n-butyl ether, the dispersibility of the metal oxide nanoparticles may decrease due to the low compatibility between the non-alcoholic solvent and the glycol-based solvent. Furthermore, the inventors have found that when an inkjet ink composition comprising metal oxide nanoparticles dispersed as dispersion particles in a glycol-based solvent is combined with a low-viscosity organic solvent such as a non-alcoholic solvent with a small number of carbon atoms per molecule, the nozzles of the inkjet head are prone to clogging, for example, when inkjet printing is continued for a long period of time or when there is a long period between the end of one inkjet print and the start of the next.

[0082] If the non-alcoholic solvent added to an inkjet ink composition containing a glycol-based solvent has 9 or fewer carbon atoms per molecule, the viscosity and surface tension of the inkjet ink composition can be reduced without causing the compatibility problems mentioned above. Therefore, excellent dispersion stability and excellent inkjet printability can be achieved simultaneously.

[0083] Furthermore, if the non-alcoholic solvent added to the inkjet ink composition containing a glycol-based solvent has seven or more carbon atoms per molecule, even if the dispersed particles are metal oxide nanoparticles, it is possible to prevent unwanted drying of the inkjet ink composition at or near the nozzle of the inkjet head. Therefore, it is possible to prevent nozzle clogging caused by this drying, and to prevent uneven coating caused by unstable ejection.

[0084] Therefore, using this inkjet ink composition makes it less likely to encounter problems associated with forming a layer made of metal oxide nanoparticles using the inkjet printing method.

[0085] Furthermore, if the inkjet ink composition does not contain additives, no additives or their decomposition products will remain in the coating film after baking, i.e., the layer consisting of the cured product of the inkjet ink composition. Therefore, when using the above-mentioned inkjet ink composition, no degradation in the performance of the light-emitting element due to residue will occur.

[0086] The tests conducted in connection with the present invention are described below.

[0087] (1) Preparation of Inkjet Ink Composition (1.1) Example 1 An inkjet ink composition containing metal oxide nanoparticles and a dispersion medium was prepared. As the metal oxide nanoparticles, nickel(II) oxide nanoparticles with an average particle size of 30 nm as determined by dynamic light scattering were used. The amount of metal oxide nanoparticles was adjusted so that their proportion in the inkjet ink composition was 1% by mass. Ethylene glycol (EG) and dipropylene glycol dimethyl ether (DMM) were used as the dispersion medium. The proportion of dipropylene glycol dimethyl ether in the dispersion medium was 15% by mass.

[0088] (1.2) Example 2 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, 3-methoxybutyl acetate (MBA) was used instead of dipropylene glycol dimethyl ether (DMM).

[0089] (1.3) Example 3 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, dipropylene glycol methyl ether acetate (DPMA) was used instead of dipropylene glycol dimethyl ether (DMM), and the proportion of dipropylene glycol methyl ether acetate in the dispersion medium was set to 10% by mass.

[0090] (1.4) Example 4 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, diethylene glycol methyl ethyl ether (DMEE) was used instead of dipropylene glycol dimethyl ether (DMM), and the proportion of diethylene glycol methyl ethyl ether in the dispersion medium was set to 20% by mass.

[0091] (1.5) Example 5 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, propylene glycol diacetate (PDGA) was used instead of dipropylene glycol dimethyl ether (DMM), and the proportion of propylene glycol diacetate in the dispersion medium was set to 12.5% ​​by mass.

[0092] (1.6) Comparative Example 1 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, instead of using ethylene glycol (EG) and dipropylene glycol dimethyl ether (DMM) as the dispersion medium, only ethylene glycol (EG) was used.

[0093] (1.7) Comparative Example 2 An inkjet ink composition was prepared in the same manner as in Example 1, except as follows: In this example, propylene glycol monomethyl ether acetate (PGMEA) was used instead of dipropylene glycol dimethyl ether (DMM).

[0094] (2) Evaluation (2.1) Dispersibility For each of the inkjet ink compositions according to Examples 1 to 5 and Comparative Examples 1 and 2, the average particle size of metal oxide nanoparticles immediately after manufacturing was measured. The average particle size was measured by dynamic light scattering. A Nanotrac® UPA-EX150 particle size analyzer manufactured by Nikkiso Co., Ltd. was used to measure the average particle size.

[0095] (2.2) Suitability for inkjet printing (2.2.1) Surface tension measurement 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 and 2. A CBVP-Z type surface tensimeter manufactured by Kyowa Interface Science Co., Ltd. was used for this measurement.

[0096] (2.2.2) Viscosity Measurement The viscosity of each of the inkjet ink compositions according to Examples 1 to 5 and Comparative Examples 1 and 2 was measured at 25°C. A TVE-22LT viscometer manufactured by Toki Sangyo Co., Ltd. was used for this measurement.

[0097] (2.2.3) Evaluation of inkjet printability Inkjet ink compositions having a viscosity at 25°C in the range of 5 mPa·s to 14 mPa·s and a surface tension in the range of 25 mN / m to 35 mN / m were evaluated as "AA" for inkjet printability.

[0098] Furthermore, inkjet ink compositions that did not meet the above conditions but had a viscosity at 25°C in the range of 1 mPa·s to 20 mPa·s and a surface tension in the range of 20 mN / m to 45 mN / m were evaluated as "A" for inkjet printability.

[0099] The other inkjet ink compositions were rated "B" for their inkjet printability.

[0100] (2.3) Each of the inkjet ink compositions according to Examples 1 to 5 and Comparative Examples 1 and 2 was dropped into a glass petri dish whose mass had been measured immediately after its manufacture. The sum of the mass M1 of the inkjet ink composition and the mass M0 of the glass petri dish was then measured. Next, each of the glass petri dishes that contained the inkjet ink composition was placed on a hot plate set to a temperature of 40°C. After 30 minutes, the sum of the mass M2 of the inkjet ink composition and the mass M0 of the glass petri dish was measured again. From the results of these measurements, the mass loss rate of the inkjet ink composition (M1 - M2) / M1 was calculated.

[0101] Inkjet ink compositions with a mass loss rate of less than 3% were evaluated as "AA" for drying resistance. Inkjet ink compositions with a mass loss rate of 3% or more but less than 4.5% were evaluated as "A" for drying resistance. Inkjet ink compositions with a mass loss rate of 4.5% or more were evaluated as "B" for drying resistance.

[0102] (2.4) Summary of Evaluation The results of the above evaluation are shown in Table 1 below. In Table 1, the values ​​listed in the columns to the right of the column labeled "Metal Oxide Nanoparticles" represent the percentage of the mass of metal oxide nanoparticles relative to the mass of the inkjet ink composition. In Table 1, the dispersion media are each indicated by an abbreviation, and the values ​​listed in the columns to the right of the column labeled with the abbreviation represent the percentage of the mass of the dispersion media indicated by the abbreviation relative to the total mass of the dispersion media. In Table 1, for dispersion media other than ethylene glycol, the number of carbon atoms per molecule is indicated in parentheses following each abbreviation.

[0103]

[0104] As shown in Table 1, the inkjet ink compositions according to Examples 1 to 5 had a sufficiently small average particle size and excellent inkjet printability and drying resistance.

[0105] In contrast, the inkjet ink composition according to Comparative Example 1 had a sufficiently small average particle size and excellent drying resistance, but failed to achieve high inkjet printability. Furthermore, the inkjet ink composition according to Comparative Example 2 had a sufficiently small average particle size and achieved high inkjet printability, but its drying resistance was insufficient.

[0106] 1...Display device, 11...Substrate, 12...Anode, 13...Blocking layer, 14...Hole injection layer, 15...Hole transport layer, 16...Light-emitting layer, 17...Electron transport layer, 18...Cathode, PXB...Third subpixel, PXG...Second subpixel, PXR...First subpixel.

Claims

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 comprising a glycol-based solvent and a non-alcohol-based solvent having 7 to 9 carbon atoms. An inkjet ink composition containing the following: 　 The inkjet ink composition according to claim 1, wherein the ratio of the mass of the non-alcoholic solvent to the total mass of the glycol-based solvent and the non-alcoholic solvent is within the range of 5% by mass to 35% by mass. 　 The inkjet ink composition according to claim 1 or 2, wherein the non-alcoholic solvent comprises one or more selected from the group consisting of 3-methoxybutyl acetate, diethylene glycol methyl ethyl ether, propylene glycol diacetate, dipropylene glycol dimethyl ether, and dipropylene glycol methyl ether acetate. 　 The inkjet ink composition according to any one of claims 1 to 3, 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. 　 The inkjet ink composition according to any one of claims 1 to 4, comprising the metal oxide nanoparticles in a concentration within the range of 0.05% by mass to 20% by mass. 　 The inkjet ink composition according to any one of claims 1 to 5, wherein the metal oxide nanoparticles comprise one or more of a plurality of nanoparticles, each containing bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide. 　 The inkjet ink composition according to any one of claims 1 to 6, wherein the metal oxide nanoparticles comprise one or more nanoparticles containing nickel oxide, nanoparticles containing zinc oxide, and nanoparticles containing magnesium-doped zinc oxide. 　 The inkjet ink composition according to any one of claims 1 to 7, wherein the metal oxide nanoparticles have an average particle size in the range of 3 nm to 50 nm as determined by dynamic light scattering. 　 The ratio of the mass of the non-alcoholic solvent to the total mass of the glycol-based solvent and the non-alcoholic solvent is within the range of 5% to 35% by mass. The non-alcoholic solvent comprises one or more selected from the group consisting of 3-methoxybutyl acetate, diethylene glycol methyl ethyl ether, propylene glycol diacetate, dipropylene glycol dimethyl ether, and dipropylene glycol methyl ether acetate. The metal oxide nanoparticles are contained in a concentration ranging from 0.05% by mass to 20% by mass. The inkjet ink composition according to any one of claims 1, 4, 6, and 7, wherein the metal oxide nanoparticles have an average particle size in the range of 3 nm to 50 nm as determined by dynamic light scattering. 　 The inkjet ink composition according to any one of claims 1 to 9 is applied to a substrate by an inkjet printing method to form a coating film, The aforementioned coating film is cured to form a functional layer. A method for manufacturing a container containing [a specific component]. 　 The manufacturing method according to claim 10, wherein the functional layer is one of a hole injection layer, a hole transport layer, and an electron transport layer. 　 A display device comprising one or more layers, each made from a cured product of an inkjet ink composition according to any one of claims 1 to 9. 　 The display device according to claim 12, 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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