Inkjet ink composition

Abstract

Provided is a technique capable of contributing to performance improvement of a light-emitting element having a layer composed of metal oxide nanoparticles and disposed between a cathode and an anode. More specifically, an inkjet ink composition according to the present embodiment contains: metal oxide nanoparticles comprising 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 a Hansen solubility parameter with a hydrogen bond term δH of 8 or more.

Description

Inkjet ink composition

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

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

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

[0004] 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.

[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, and a dispersion medium containing a glycol-based solvent and a non-alcohol-based solvent having a hydrogen bonding term δH of the Hansen solubility parameter of 8 or more.

[0006] According to another aspect of the present invention, there is provided the ink-jet ink composition according to the above aspect, wherein the δH of the non-alcoholic solvent is 30 or less.

[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, 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.

[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 include at least one of nanoparticles containing nickel oxide, nanoparticles containing zinc oxide, and nanoparticles containing magnesium-doped zinc oxide.

[0009] 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.

[0010] According to yet another aspect of the present invention, there is provided an ink-jet ink composition according to any one of the above aspects, wherein the content of the metal oxide nanoparticles is in the range of 0.05 to 20% by weight.

[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 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, where R1 represents the total content (% by mass) of the glycol-based solvents relative to the dispersion medium, and R2 represents the total content (% by mass) of the non-alcohol-based solvents relative to the dispersion medium.

[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 glycol-based solvent is one or more selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, triethylene glycol, and hexylene glycol.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] According to yet another aspect of the present invention, there is provided a display device according to any of the above aspects, wherein the one or more functional layers include a hole injection layer or a hole transport layer.

[0019] 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.

[0020] FIG. 1 is a cross-sectional view of a display device according to one embodiment of the present invention.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] <1> Display Device Fig. 1 is a cross-sectional view of a display device according to one embodiment of the present invention. The display device 1 shown in Fig. 1 employs an active matrix driving method and is capable of displaying color images.

[0025] The display device 1 includes a plurality of pixels arranged in the X and Y directions described below. Each pixel includes a first sub-pixel PXR, a second sub-pixel PXG, and a third sub-pixel PXB. Each of the first sub-pixel PXR, the second sub-pixel PXG, and the third sub-pixel PXB includes a light-emitting element and a pixel circuit. Here, as an example, it is assumed that the semiconductor included in the light-emitting element is inorganic.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] When the substrate 11 is light-transmitting, the display device 1 may be of a top emission type or a bottom emission type, whereas when the substrate 11 is light-shielding, the display device 1 is of a top emission type.

[0031] 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.

[0032] When the display device 1 is a top-emission type, the anode 12 preferably includes a light-reflecting layer. The light-reflecting layer is made of, for example, an elemental metal such as aluminum or silver, or an alloy containing one or more of these. A layer made of a metal such as an elemental metal or an alloy can be formed by, for example, a vacuum deposition method.

[0033] 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.

[0034] The partition wall layer 13 is provided on the substrate 11 and the anodes 12. The partition wall layer 13 has through holes at the positions of the anodes 12. Each of these through holes has a shape that tapers from the upper opening to the lower opening. The peripheral edge of each anode 12 is covered with the partition wall layer 13, and the central part is exposed to the internal space of the through hole provided in the partition wall layer 13.

[0035] The partition wall layer 13 is made of an insulating material. According to one example, the partition wall layer 13 is made of an inorganic insulating material. According to another example, the partition wall layer 13 is made of a cured resin.

[0036] 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.

[0037] The hole injection layer 14 is made of a hole injection material, such as nickel oxide (NiO) or bismuth oxide (BiO). ２ O ３ ), cobalt oxide (CoO), copper oxide (Cu ２ O), molybdenum oxide (MoO ３ The hole injection material made of these metal oxides can be contained in the hole injection layer 14 in the form of metal oxide nanoparticles.

[0038] 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. Metal oxide nanoparticles preferably have an average particle diameter in the range of 3 nm to 50 nm as measured by dynamic light scattering.

[0039] 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.

[0040] 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.

[0041] The hole transport layer 15 is made of a hole transport material. The hole transport material is, for example, bismuth oxide (Bi ２ O ３ ), cobalt oxide (CoO), copper oxide (Cu ２ O), molybdenum oxide (MoO ３ The hole injection material made of these metal oxides may be contained in the hole transport layer 15 in the form of metal oxide nanoparticles. The average particle diameter of these metal oxide nanoparticles, as measured by dynamic light scattering, is preferably within the range described above for the hole injection material.

[0042] 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.

[0043] The light-emitting layer 16 covers the hole transport layer 15 in the through-holes provided in the partition layer 13. The light-emitting layer 16 typically has a larger ionization energy than the ionization energy of the hole transport layer 15 and a larger electron affinity than the electron affinity of the hole transport layer 15.

[0044] The light-emitting layer 16 is made of a light-emitting material. The light-emitting layers 16 of the first sub-pixel PXR, the second sub-pixel PXG, and the third sub-pixel PXB contain different light-emitting materials. For example, the light-emitting layer 16 of the first sub-pixel PXR, the second sub-pixel PXG, and the third sub-pixel PXB use a light-emitting material that emits red light, a light-emitting material that emits green light, and a light-emitting material that emits blue light, respectively.

[0045] According to one example, the light-emitting material is a quantum dot, which is a semiconductor particle having, for example, a core-shell structure and a particle size ranging from a few nanometers to about 10 nanometers.

[0046] 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.

[0047] The shell is a thin layer epitaxially grown on the surface of the core, having a thickness of 1 to 4 atoms. The shell contributes to improving and stabilizing the luminous efficiency. The shell may have a single-layer structure or a multi-layer structure.

[0048] 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.

[0049] Another example of quantum dots is a quantum dot with a core made of ZnSeTe, covered with a first shell made of ZnSe, and covered with a second shell made of ZnS. Such quantum dots emit blue light when their particle size is small.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] The cathode 18 covers the electron transport layer 17 and the exposed portion of the partition wall layer 13. In this example, the cathode 18 is a common electrode facing the plurality of anodes 12.

[0056] When the display device 1 is a bottom-emission type, the cathode 18 preferably includes a light-reflecting layer. The light-reflecting layer is made of, for example, an elemental metal such as aluminum or silver, or an alloy containing one or more of these. A layer made of a metal such as an elemental metal or an alloy can be formed by, for example, a vacuum deposition method.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] <2> Manufacturing Method of Display Device The display device 1 shown in FIG. 1 can be manufactured, for example, by the following method.

[0062] First, a structure including a substrate 11, an anode 12, and a partition layer 13 is prepared.

[0063] 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.

[0064] Next, the light-emitting layer 16 is formed. As described above, the light-emitting layers 16 of the first sub-pixel PXR, the second sub-pixel PXG, and the third sub-pixel PXB are made of different light-emitting materials. Therefore, the light-emitting layer 16 of the first sub-pixel PXR, the second sub-pixel PXG, and the third sub-pixel PXB are formed separately. Each of these light-emitting layers 16 can be formed by using, for example, a lift-off method.

[0065] 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.

[0066] Next, the cathode 18 is formed. The cathode 18 can be formed by vacuum deposition, sputtering, or a combination thereof. Thereafter, the light-emitting element is sealed, if necessary. In this manner, the display device 1 shown in the figure is obtained.

[0067] <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.

[0068] 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.

[0069] That is, a suitably used inkjet ink composition contains metal oxide nanoparticles and a dispersion medium containing 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.

[0070] 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. The metal oxide nanoparticles may be those described above for the hole injection layer 14, the hole transport layer 15, and the electron transport layer 17.

[0071] 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.

[0072] The proportion of metal oxide nanoparticles in the inkjet ink composition is preferably in the range of 0.05% by mass to 20% by mass, more preferably in the range of 0.1% by mass to 10% by mass, and even more preferably in the range of 0.5% by mass to 5% by mass.

[0073] The dispersion medium contains a glycol-based solvent. By including a glycol-based solvent in the dispersion medium, the solvent becomes excellent in dispersibility of metal oxide nanoparticles. The glycol-based solvent is preferably a glycol-based solvent having a hydrogen bond parameter δH of the Hansen solubility parameter (HSP) of 14 or more. A glycol-based solvent having a δH of 14 or more is particularly excellent in dispersion stability of nanoparticles. The dispersion medium contains, as a glycol-based solvent having a hydrogen bond parameter δH of 14 or more, for example, one or more selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, triethylene glycol, and hexylene glycol. The upper limit of δH of the glycol-based solvent may be, for example, 30 or less.

[0074] 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.

[0075] Here, the Hansen solubility parameter (HSP) is a solubility parameter introduced by Hildebrand, divided into three components: a dispersion term δD, a polar term δP, and a hydrogen bonding term δH. The dispersion term δD represents the energy due to intermolecular dispersion forces, the polar term δP represents the energy due to intermolecular dipole interactions, and the hydrogen bonding term δH represents the energy due to intermolecular hydrogen bonds.

[0076] Examples of non-alcoholic solvents include aprotic solvents such as amide compounds, aliphatic ester compounds, aliphatic ether compounds, and sulfoxide compounds. As described above, the hydrogen bond parameter δH of HSP in a non-alcoholic solvent is 8 or more, preferably 10 or more. If the hydrogen bond parameter δH of HSP in a non-alcoholic solvent is low, the inkjet printability may be improved, but dispersibility may be deteriorated. The higher the hydrogen bond parameter δH of a non-alcoholic solvent, the better the dispersibility, which is preferable. Therefore, the upper limit of the hydrogen bond parameter δH of a non-alcoholic solvent is not particularly limited, but may be, for example, 30 or less.

[0077] Examples of non-alcoholic solvents having a hydrogen bond parameter δH of 8 or greater for HSP include N,N-dimethylformamide (DMF) (δH 11.3), tetramethylurea (δH 11), dimethyl sulfoxide (DMSO) (δH 10.2), propylene glycol monomethyl ether acetate (PGMEA or PGMAc) (δH 9.8), N,N-dimethylacetamide (DMA) (δH 9.4), sulfolane (δH 8.7), hexamethylphosphoric triamide (HMPA) (δH 8.7), 3-methoxybutyl acetate (δH 8.1), and tetrahydrofuran (THF) (δH 8.0). In one embodiment, the dispersion medium contains one or more non-alcoholic solvents selected from these.

[0078] The blending ratio of the glycol solvent to the non-alcohol solvent contained in the dispersion medium preferably satisfies 0.10≦R2 / (R1+R2)≦0.50, and more preferably satisfies 0.15≦R2 / (R1+R2)≦0.30, where R1 represents the total content (mass%) of the glycol solvents relative to the dispersion medium, and R2 represents the total content (mass%) of the non-alcohol solvents relative to the dispersion medium.

[0079] The dispersion medium may further contain a solvent other than the glycol-based solvent and the non-alcohol-based solvent having a δH of 8 or more, as long as it does not affect the above-mentioned effects, i.e., the compatibility of inkjet printability and dispersion stability. The total proportion of the glycol-based solvent and the non-alcohol-based solvent having a δH of 8 or more in the dispersion medium is preferably in the range of 50% by mass to 100% by mass, more preferably in the range of 65% by mass to 100% by mass, even more preferably in the range of 80% by mass to 100% by mass, and particularly preferably 100% by mass.

[0080] The proportion of the dispersion medium in the ink-jet ink composition is preferably in the range of 80% to 99% by mass, and more preferably in the range of 85% to 99% by mass.

[0081] 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 45 mN / m. The surface tension of the ink-jet ink composition at 25° C. is preferably in the range of 25 mN / m to 35 mN / m.

[0082] In addition, the ink-jet ink composition has a viscosity at 25° C. of, for example, 20 mPa·s or less.

[0083] The dispersion medium of this inkjet ink composition 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 glycol-based solvents generally have high viscosity and large surface tension, resulting in poor ink ejection properties and making them unsuitable for forming coating films.

[0084] Adding other solvents, such as isopropyl alcohol (IPA) or ethyl acetate (AcOEt), to a dispersion medium containing a glycol-based solvent to adjust the viscosity and surface tension reduces the viscosity and surface tension, but also reduces the dispersion stability of metal oxide nanoparticles.

[0085] The inkjet ink composition described above, which contains a glycol-based solvent and a non-alcohol-based solvent having a Hansen solubility parameter (HSP) hydrogen bond term δH of 8 or more 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, 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. It is surprising that this effect can be achieved simply by combining a specific dispersion solvent without using a dispersant such as an alcohol amine.

[0086] 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.

[0087] Tests conducted in connection with the present invention are described below. <1> Preparation of Inkjet Ink Composition <1.1> Example 1 An inkjet ink composition containing metal oxide nanoparticles and a dispersion medium was prepared. The metal oxide nanoparticles used were nickel (II) oxide nanoparticles with an average particle diameter of 30 nm. The average particle diameter of the metal oxide nanoparticles was measured by the dynamic light scattering method described below. The amount of metal oxide nanoparticles was adjusted so that the proportion of metal oxide nanoparticles in the inkjet ink composition was 1% by mass.

[0088] Ethylene glycol (EG) and propylene glycol monomethyl ether acetate (PGMAc) were used as dispersion media, and the blending ratio of the two solvents was adjusted to 85% by mass of EG and 15% by mass of PGMAc.

[0089] <1.2> Example 2 An inkjet ink composition similar to that of Example 1 was prepared, except for the following: In this example, nickel(II) oxide nanoparticles having an average particle size of 20 nm were used instead of nickel(II) oxide nanoparticles having an average particle size of 30 nm.

[0090] <1.3> Example 3 An inkjet ink composition similar to that of Example 1 was prepared, except for the following: In this example, nickel(II) oxide nanoparticles having an average particle size of 50 nm were used instead of nickel(II) oxide nanoparticles having an average particle size of 30 nm.

[0091] <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, a mixed solvent of ethylene glycol (EG), propylene glycol monomethyl ether acetate (PGMAc), and N,N-dimethylformamide (DMF) was used as the dispersion medium instead of the mixed solvent of ethylene glycol (EG) and propylene glycol monomethyl ether acetate (PGMAc). The mixing ratio of the three solvents was adjusted to 75% by mass of EG, 15% by mass of PGMAc, and 10% by mass of DMF.

[0092] <1.5> Example 5 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions. In this example, a mixed solvent of ethylene glycol (EG) and N,N-dimethylformamide (DMF) was used as the dispersion medium instead of a mixed solvent of ethylene glycol (EG) and propylene glycol monomethyl ether acetate (PGMAc). The mixing ratio of the two solvents was adjusted to 50% by mass of EG and 50% by mass of DMF.

[0093] <1.6> Example 6 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions. In this example, a mixed solvent of ethylene glycol (EG) and N,N-dimethylformamide (DMF) was used as the dispersion medium instead of a mixed solvent of ethylene glycol (EG) and propylene glycol monomethyl ether acetate (PGMAc). The mixing ratio of the two solvents was adjusted to 80% by mass of EG and 20% by mass of DMF.

[0094] <1.7> Example 7 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions. In this example, a mixed solvent of ethylene glycol (EG) and N,N-dimethylformamide (DMF) was used as the dispersion medium instead of a mixed solvent of ethylene glycol (EG) and propylene glycol monomethyl ether acetate (PGMAc). The mixing ratio of the two solvents was adjusted to 90% by mass of EG and 10% by mass of DMF.

[0095] <1.8> Example 8 An inkjet ink composition was prepared in the same manner as in Example 1, except for the following points: In this example, the inkjet ink composition was adjusted so that the proportion of metal oxide nanoparticles (NiO) in the inkjet ink composition was 3 mass %.

[0096] <1.9> Comparative Example 1 An inkjet ink composition similar to that of Example 1 was prepared, except for the following: In this example, ethylene glycol (EG) alone was used as the dispersion medium instead of a mixed solvent of ethylene glycol (EG) and propylene glycol monomethyl ether acetate (PGMAc).

[0097] <1.10> Comparative Example 2 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions: In this example, a mixed solvent of ethylene glycol (EG) and isopropyl alcohol (IPA) was used as the dispersion medium instead of a mixed solvent of ethylene glycol (EG) and propylene glycol monomethyl ether acetate (PGMAc). The mixing ratio of the two solvents was adjusted to 80% by mass of EG and 20% by mass of IPA.

[0098] <1.11> Comparative Example 3 An inkjet ink composition similar to that of Example 1 was prepared, with the following exceptions: In this example, a mixed solvent of ethylene glycol (EG) and propylene glycol monomethyl ether acetate (PGMAc) was replaced with a mixed solvent of ethylene glycol (EG) and ethyl acetate (AcOEt) as the dispersion medium. The mixing ratio of the two solvents was adjusted to 80% by mass of EG and 20% by mass of AcOEt.

[0099] <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 7 and Comparative Examples 1 to 3. 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.

[0100] Furthermore, each of the inkjet ink compositions according to Examples 1 to 7 and Comparative Examples 1 to 3 was allowed to stand for 720 hours in an environment at 5° C. immediately after preparation. Thereafter, the average particle size of the metal oxide nanoparticles was measured using the same method as above.

[0101] The average particle diameter D immediately after preparation ０ Average particle diameter D after standing for 720 hours ７２０ and average particle diameter D ０ The ratio of the difference between ７２０ -D ０ ) / D ０ was calculated as the particle size change rate. Inkjet ink compositions whose particle size change rate was less than 0.10 were evaluated as "A" for dispersion stability. Inkjet ink compositions whose particle size change rate was 0.10 or more were evaluated as "B" for dispersion stability.

[0102] <2.2> Inkjet Printing Suitability <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 7 and Comparative Examples 1 to 3. A CBVP-Z type surface tensiometer manufactured by Kyowa Interface Science Co., Ltd. was used for this measurement.

[0103] <2.2.2> Viscosity Measurement The viscosity at 25° C. was measured for each of the inkjet ink compositions according to Examples 1 to 7 and Comparative Examples 1 to 3. A TVE-22LT viscometer manufactured by Toki Sangyo Co., Ltd. was used for this measurement.

[0104] <2.2.3> Evaluation of Inkjet Printability Inkjet ink compositions that had 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.

[0105] 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 45 mN / m were evaluated as "A" for inkjet printability.

[0106] The other inkjet ink compositions were rated "B" for inkjet printability.

[0107] <2.3> Summary of Evaluation The results of the above evaluation are shown in Table 1 below.

[0108]

[0109] As shown in Table 1, the inkjet ink composition according to Comparative Example 1, which used only ethylene glycol (EG) as the dispersion medium, had excellent dispersion stability of the metal oxide nanoparticles, but was inferior in inkjet printability.

[0110] Furthermore, the inkjet ink compositions according to Comparative Example 2, which used isopropyl alcohol (IPA), an alcohol, as a solvent used in combination with ethylene glycol (EG) as a dispersion medium, and Comparative Example 3, which used ethyl acetate (AcOEt), whose HSP δH is less than 8, were excellent in inkjet printability, but were inferior in dispersion stability of the metal oxide nanoparticles.

[0111] In contrast, the inkjet ink compositions of Examples 1 to 8 were excellent in dispersion stability of metal oxide nanoparticles and inkjet printability. The inkjet ink compositions of Examples 1 to 4 and 8 were particularly excellent in inkjet printability.

[0112] The ethylene glycol used as the glycol solvent in Examples 1 to 8 has a high δH, with an HSP [δD, δP, δH] of [δD = 17, δP = 11, δH = 26]. Diethylene glycol, propylene glycol, trimethylene glycol, triethylene glycol, and hexylene glycol, which were previously listed as preferred glycol solvents along with ethylene glycol, have a δH of 14 or more, which is high similar to that of ethylene glycol. Furthermore, these glycol solvents are low-molecular-weight alkylene glycols having 6 or fewer carbon atoms and have a molecular structure similar to that of ethylene glycol. The inventors arbitrarily selected propylene glycol [δD=16.8, δP=10.4, δH=21.3] and trimethylene glycol [δD=16.8, δP=13.5, δH=23.2] from the glycol-based solvents described above, and prepared 1% by mass dispersions of NiO (average particle size: 30 nm) for each of these glycol-based solvents and ethylene glycol, and measured the particle size distribution. As a result, it was confirmed that propylene glycol and trimethylene glycol exhibited the same particle size distribution as ethylene glycol and exhibited the same dispersion stability as ethylene glycol.

[0113] From these, it can be easily inferred that, even when any one selected from diethylene glycol, propylene glycol, trimethylene glycol, triethylene glycol, and hexylene glycol is used in place of ethylene glycol in Examples 1 to 8, an inkjet ink composition exhibiting the same effects as those of Examples 1 to 8 can be obtained.

[0114] 1...display device, 11...substrate, 12...anode, 13...partition layer, 14...hole injection layer, 15...hole transport layer, 16...light-emitting layer, 17...electron transport layer, 18...cathode, PXB...third sub-pixel, PXG...second sub-pixel, PXR...first sub-pixel.

Claims

1. An inkjet ink composition comprising 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 a hydrogen bonding term δH of the Hansen solubility parameter of 8 or more.

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

3. The ink-jet ink composition according to claim 1 or 2, wherein the metal oxide nanoparticles comprise 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.

4. The ink-jet ink composition according to any one of claims 1 to 3, wherein the metal oxide nanoparticles comprise at least one of nanoparticles containing nickel oxide, nanoparticles containing zinc oxide, and nanoparticles containing magnesium-doped zinc oxide.

5. The ink-jet ink composition according to any one of claims 1 to 4, wherein the metal oxide nanoparticles have an average particle diameter in the range of 3 nm to 50 nm as determined by dynamic light scattering.

6. The ink-jet ink composition according to any one of claims 1 to 5, wherein the content of the metal oxide nanoparticles is in the range of 0.05 to 20% by mass.

7. The inkjet ink composition according to any one of claims 1 to 6, 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, where 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.

8. The ink-jet ink composition according to any one of claims 1 to 7, wherein the glycol-based solvent is one or more selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, triethylene glycol, and hexylene glycol.

9. The ink-jet ink composition according to any one of claims 1 to 8, wherein the non-alcoholic solvent is one or more selected from the group consisting of amide compounds, aliphatic ester compounds, and aliphatic ether compounds.

10. A method for manufacturing a display device, comprising: applying the inkjet ink composition according to any one of claims 1 to 9 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.

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

12. A display device comprising one or more functional layers each made of a cured product of the ink-jet ink composition according to any one of claims 1 to 9.

13. The display device 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. The display device according to claim 12, wherein the one or more functional layers include a hole injection layer or a hole transport layer.

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