Method for producing 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. A method for producing an inkjet ink composition includes preparing a dispersion containing metal oxide nanoparticles and a glycol-based solvent, and mixing the dispersion with a non-alcohol-based solvent.

Description

[Technical Field]

[0001] The present invention relates to the preparation of 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 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] International Publication No. 2022 / 070296 Summary of the Invention [Problem to be solved by the invention]

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

[0005] According to one aspect of the present invention, there is provided a method for producing an inkjet ink composition, the method comprising: preparing a dispersion containing metal oxide nanoparticles and a glycol-based solvent; and mixing the dispersion with a non-alcohol-based solvent.

[0006] According to another aspect of the present invention, there is provided a method for producing an ink-jet ink composition according to the above aspect, wherein 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.

[0007] According to yet another aspect of the present invention, there is provided a method for producing 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, and titanium oxide.

[0008] According to yet another aspect of the present invention, there is provided a method for producing 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.

[0009] According to yet another aspect of the present invention, there is provided a method for producing an ink-jet ink composition according to any 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 a dynamic light scattering method.

[0010] According to yet another aspect of the present invention, there is provided a method for producing an ink-jet ink composition according to any of the above aspects, which obtains an ink-jet ink composition containing the metal oxide nanoparticles at a concentration in the range of 0.05% by mass to 20% by mass.

[0011] According to yet another aspect of the present invention, the mass M of the glycol-based solvent A and the mass M of the non-alcoholic solvent B The mass M of the non-alcoholic solvent in the total B Percentage of M B / (M A +M B ) is in the range of 0.10 to 0.50.

[0012] According to yet another aspect of the present invention, there is provided a method for producing an ink-jet ink composition according to any of the above aspects, wherein the glycol solvent is one or more selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, and hexylene glycol.

[0013] According to yet another aspect of the present invention, there is provided a method for producing an 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 an ink-jet ink composition produced by the production method according to any of the above aspects.

[0015] According to yet another aspect of the present invention, there is provided a method for forming a printed layer, the method including: producing an inkjet ink composition by the production method according to any one of the above aspects; and supplying the inkjet ink composition to a surface of a substrate by inkjet printing to form a coating film.

[0016] According to yet another aspect of the present invention, there is provided a printed layer formed by the forming method according to the above aspect.

[0017] According to yet another aspect of the present invention, there is provided a display device including the print layer according to the above aspect.

[0018] According to yet another aspect of the present invention, there is provided a method for manufacturing a display device, which includes forming a print layer by the forming method according to the above aspect. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0020] [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

[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 is a display device that 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, the semiconductor included in the light-emitting element is assumed to be 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, and 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. Layers made of metals such as elemental metals and alloys can be formed by, for example, vacuum deposition.

[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 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 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.

[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 insulator. 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. 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.

[0038] 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.

[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. 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.

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

[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 nm to about 10 nm.

[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, 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.

[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 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.

[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. 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.

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

[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> Display device manufacturing method 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 sequence. Each of the hole injection layer 14 and the hole transport layer 15 can be formed, for example, by inkjet printing 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 inkjet printing to form a coating film. Next, this coating film is dried. For example, the coating film is baked. As a result, a layer made of the cured product of the inkjet ink composition is obtained as a printed layer.

[0064] 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.

[0065] Next, the electron transport layer 17 is formed. As described above for the hole injection layer 14 and the hole transport layer 15, the electron transport layer 17 can be formed by, for example, 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 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.

[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 perspective, it is preferable to form one or more of the hole injection layer 14, the hole transport layer 15, and the electron transport layer 17 using an inkjet ink composition having the composition described below. That is, the inkjet ink composition that is preferably used contains metal oxide nanoparticles, a glycol-based solvent, and a non-alcohol-based solvent.

[0069] Furthermore, if the ink-jet ink composition contains an additive, and the 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. That is, it is preferable that the ink-jet ink composition contains metal oxide nanoparticles, a glycol-based solvent, and a non-alcohol-based solvent, and does not contain any other components.

[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, 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.

[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, 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.

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

[0073] The inkjet ink composition contains a glycol-based solvent as part of the dispersion medium. The glycol-based solvent 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, diethylene glycol, propylene glycol, triethylene glycol, and hexylene glycol. The glycol-based solvent preferably contains ethylene glycol, and more preferably is ethylene glycol.

[0074] The inkjet ink composition contains a non-alcoholic solvent as part of the other dispersion medium. The non-alcoholic solvent can contribute to inkjet printability. The non-alcoholic solvent is, for example, an aprotic solvent, preferably one or more selected from the group consisting of an amide compound, an aliphatic ester compound, and an aliphatic ether compound. The non-alcoholic solvent can include, for example, one or more of N,N'-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and propylene glycol monomethyl ether acetate (PGMEA or PGMAc).

[0075] Mass of glycol solvent M A and the mass of the non-alcoholic solvent M B The mass of non-alcoholic solvents in the total of B Percentage of M B / (M A +M B ) is preferably in the range of 0.10 to 0.50, and more preferably in the range of 0.15 to 0.30.

[0076] 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.

[0077] According to one example, the ink-jet ink composition has a surface tension in the range of 20 mN / m to 45 mN / m at 25° C. Preferably, the surface tension of the ink-jet ink composition in the range of 25 mN / m to 35 mN / m at 25° C.

[0078] In addition, the ink-jet ink composition has a viscosity at 25° C. of, for example, 20 mPa·s or less.

[0079] 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 viscosity and large surface tension, resulting in poor ink ejection properties and making them unsuitable for forming coating films.

[0080] Adding a non-alcoholic solvent to an inkjet ink composition containing a glycol-based solvent can adjust the viscosity and surface tension. Therefore, by appropriately adjusting the type and amount of the glycol-based solvent and non-alcoholic solvent, it is possible to simultaneously achieve excellent dispersion stability and excellent inkjet printability. 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.

[0081] Furthermore, when the inkjet ink composition does not contain any additives, the additives or their decomposition products do not remain in the coating film after baking, i.e., in the layer made of the cured product of the inkjet ink composition, and therefore, when the inkjet ink composition is used, the performance of the light-emitting element is not deteriorated due to the residue.

[0082] <4> Method for producing inkjet ink composition The inkjet ink composition can be produced, 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 the dispersion medium. Alternatively, the inkjet ink composition can be produced by first dispersing metal oxide nanoparticles in a non-alcohol-based solvent, and then mixing this dispersion with a glycol-based solvent. However, the present inventors have found that the inkjet ink compositions obtained by these methods leave room for improvement in terms of the dispersion state and dispersion stability of the metal oxide nanoparticles.

[0083] The present inventors have repeatedly produced inkjet inks using various methods and analyzed the inkjet ink compositions, and as a result have found that the following method makes it possible to produce an inkjet ink composition with excellent dispersion state and dispersion stability of metal oxide nanoparticles. Specifically, in the method for producing an inkjet ink composition according to this embodiment, first, a dispersion liquid containing metal oxide nanoparticles and a glycol-based solvent is prepared. Next, this dispersion liquid is mixed with a non-alcohol-based solvent.

[0084] The present inventors believe that the reason why the dispersion state and dispersion stability of metal oxide nanoparticles differ depending on the production method is as follows.

[0085] When metal oxide nanoparticles are mixed with a dispersion medium containing a non-alcoholic solvent, the non-alcoholic solvent hinders the dispersion of the metal oxide nanoparticles. Therefore, in the inkjet ink composition obtained by this method, immediately after production, many of the metal oxide nanoparticles form large secondary particles. Large secondary particles are prone to settling and further aggregation during storage of the inkjet ink composition. Therefore, the inkjet ink composition obtained by the method of mixing metal oxide nanoparticles with a dispersion medium containing a non-alcoholic solvent has poor dispersion state and dispersion stability of the metal oxide nanoparticles.

[0086] In contrast, mixing metal oxide nanoparticles with a glycol-based solvent in the absence of a non-alcoholic solvent results in a dispersion in which the metal oxide nanoparticles are well dispersed. Because the metal oxide nanoparticles are well dispersed in this dispersion, an inkjet ink composition obtained by mixing this dispersion with a non-alcoholic solvent also contains the metal oxide nanoparticles well dispersed. Furthermore, if the metal oxide nanoparticles have not formed large secondary particles immediately after production of the inkjet ink composition, the glycol-based solvent is capable of maintaining the metal oxide nanoparticles well dispersed. Therefore, this method allows the production of an inkjet ink composition in which the metal oxide nanoparticles are well dispersed and have excellent dispersion stability.

[0087] An inkjet ink composition having excellent dispersion state and dispersion stability of metal oxide nanoparticles is useful for reducing variations in shape and size in the formation of a printed layer. Therefore, the above manufacturing method can contribute to improving the performance of light-emitting devices having a layer of metal oxide nanoparticles between a cathode and an anode. [Example]

[0088] The following describes tests carried out in connection with the present invention.

[0089] (1) Preparation of Inkjet Ink Composition (1.1) Example 1 An inkjet ink composition comprising metal oxide nanoparticles, a glycol-based solvent, and a non-alcohol-based solvent was prepared by the following method.

[0090] First, a dispersion liquid containing metal oxide nanoparticles and a glycol-based solvent was prepared. Specifically, a glass mayonnaise bottle was first prepared as a bottle container, and metal oxide nanoparticles and a glycol-based solvent were placed in this order into the bottle container. The metal oxide nanoparticles used were nanoparticles made of nickel (II) oxide and having an average primary particle diameter of 7.8 nm. The glycol-based solvent used was ethylene glycol (EG). The amount of glycol-based solvent was 85 parts by mass relative to 100 parts by mass of the total of the glycol-based solvent and the non-alcohol-based solvent. The amount of metal oxide nanoparticles was adjusted so that the concentration of metal oxide nanoparticles in the inkjet ink composition was 1% by mass.

[0091] Next, the bottle was capped, and dispersion treatment using an ultrasonic disperser and hand shaking were alternately repeated until the metal oxide nanoparticle precipitate disappeared. Next, the cap was removed from the bottle, and zirconia beads were added to the bottle. Next, the bottle was capped, and this was subjected to dispersion treatment using a shaker.

[0092] After the 3-hour dispersion treatment, the bottle was left to stand for about 1 hour. Then, the lid was removed from the bottle, and the contents were filtered to separate the zirconia beads from the dispersion. In this way, a dispersion was obtained.

[0093] Next, this dispersion liquid was mixed with a non-alcoholic solvent. Specifically, the non-alcoholic solvent was added to the dispersion liquid in the container while stirring it with a magnetic stirrer. Propylene glycol monomethyl ether acetate (PGMEA) was used as the non-alcoholic solvent. The amount of the non-alcoholic solvent was 15 parts by mass relative to 100 parts by mass of the total of the glycolic solvent and the non-alcoholic solvent.

[0094] Stirring with the magnetic stirrer was continued for 60 minutes after the addition of the non-alcoholic solvent was completed. The contents of the vessel were then filtered through a filter with 5 μm openings. In this manner, an inkjet ink composition was obtained.

[0095] (1.2) Example 2 An inkjet ink composition comprising metal oxide nanoparticles, a glycol-based solvent, and a non-alcoholic solvent was prepared in the same manner as in Example 1, with the following exceptions: In this example, the amount of glycol-based solvent was 76 parts by mass per 100 parts by mass of the total of the glycol-based solvent and the non-alcoholic solvent. Furthermore, N,N'-dimethylformamide (DMF) and PGMEA were used as the non-alcoholic solvent. The amounts of DMF and PGMEA were 10 parts by mass and 14 parts by mass, respectively, per 100 parts by mass of the total of the glycol-based solvent and the non-alcoholic solvent.

[0096] (1.3) Comparative Example 1 An inkjet ink composition comprising metal oxide nanoparticles and a non-alcoholic solvent was prepared by the following method.

[0097] Specifically, a glass mayonnaise bottle was prepared as a bottle container, and metal oxide nanoparticles and a non-alcoholic solvent were added to the bottle container in this order. The metal oxide nanoparticles used were the same nanoparticles as those used in Example 1. PGMEA was used as the non-alcoholic solvent. The amount of metal oxide nanoparticles was adjusted so that the concentration of metal oxide nanoparticles in the inkjet ink composition was 1% by mass.

[0098] Next, the bottle was capped, and dispersion treatment using an ultrasonic disperser and hand shaking were alternately repeated until the metal oxide nanoparticle precipitate disappeared. Next, the cap was removed from the bottle, and zirconia beads were added to the bottle. Next, the bottle was capped, and this was subjected to dispersion treatment using a shaker.

[0099] After the 3-hour dispersion treatment, the bottle was left to stand for approximately 1 hour. The lid was then removed from the bottle, and the contents were filtered to separate the zirconia beads from the dispersion. The dispersion was then filtered through a filter with a 5 μm mesh size. In this manner, an inkjet ink composition was obtained.

[0100] (1.4) Comparative Example 2 An inkjet ink composition comprising metal oxide nanoparticles, a glycol-based solvent, and a non-alcohol-based solvent was prepared by the following method.

[0101] First, a dispersion medium consisting of a glycol-based solvent and a non-alcohol-based solvent was prepared. Specifically, the non-alcoholic solvent was added to the glycol-based solvent in a container while stirring it with a magnetic stirrer. EG was used as the glycol-based solvent, and DMF and PGMEA were used as the non-alcoholic solvents. The amounts of EG, DMF, and PGMEA were 76 parts by mass, 10 parts by mass, and 14 parts by mass, respectively, relative to a total of 100 parts by mass. Stirring with the magnetic stirrer was continued for 60 minutes after the addition of the non-alcoholic solvent was completed.

[0102] Next, a glass mayonnaise bottle was prepared as a bottle container, and the metal oxide nanoparticles and the above-mentioned dispersion medium were poured into the bottle container in this order. The metal oxide nanoparticles used were the same nanoparticles as those used in Example 1. The amount of the metal oxide nanoparticles was adjusted so that the concentration of the metal oxide nanoparticles in the inkjet ink composition was 1% by mass.

[0103] Next, the bottle was capped, and dispersion treatment using an ultrasonic disperser and hand shaking were alternately repeated until the metal oxide nanoparticle precipitate disappeared. Next, the cap was removed from the bottle, and zirconia beads were added to the bottle. Next, the bottle was capped, and this was subjected to dispersion treatment using a shaker.

[0104] After the 3-hour dispersion treatment, the bottle was left to stand for approximately 1 hour. The lid was then removed from the bottle, and the contents were filtered to separate the zirconia beads from the dispersion. The dispersion was then filtered through a filter with a 5 μm mesh size. In this manner, an inkjet ink composition was obtained.

[0105] (2) Evaluation (2.1) Dispersion state / dispersion stability The average particle size of the metal oxide nanoparticles was measured immediately after production for each of the inkjet ink compositions of Examples 1 and 2 and Comparative Examples 1 and 2. The average particle size was measured by dynamic light scattering. A Nanotrac (registered trademark) UPA-EX150 particle size distribution analyzer manufactured by Nikkiso Co., Ltd. was used to measure the average particle size.

[0106] Furthermore, each of the inkjet ink compositions according to Examples 1 and 2 and Comparative Examples 1 and 2 was allowed to stand for 720 hours in an environment at 25°C immediately after production, after which the average particle size of the metal oxide nanoparticles was measured using the same method as above.

[0107] Next, the average particle diameter D after standing for 720 hours was compared with the average particle diameter D immediately after production. 720 and the average particle diameter D0 (D 720 -D0) / D0 was calculated as the particle size change rate. 720 Inkjet ink compositions in which the ratio (D −D0) / D0 was less than 0.10 were evaluated as “A” for dispersion state / dispersion stability. 720 Inkjet ink compositions in which −D0) / D0 was 0.10 or greater were evaluated as “B” for dispersion state / dispersion stability.

[0108] (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 and 2 and Comparative Examples 1 and 2. For this measurement, a CBVP-Z type surface tensiometer manufactured by Kyowa Interface Science Co., Ltd. was used.

[0109] (2.2.2) Viscosity measurement The viscosity at 25° C. was measured for each of the inkjet ink compositions according to Examples 1 and 2 and Comparative Examples 1 and 2. A TVE-22LT viscometer manufactured by Toki Sangyo Co., Ltd. was used for this measurement.

[0110] (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.

[0111] 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 rated "A" for inkjet printability.

[0112] The other inkjet ink compositions were rated "B" for inkjet printability.

[0113] (2.3) Summary of evaluation The results of the above evaluations are shown in Table 1 below.

[0114] [Table 1]

[0115] As shown in Table 1, the inkjet ink compositions of Examples 1 and 2 had sufficiently small average particle sizes immediately after production, and were excellent in dispersion stability and inkjet printing suitability.

[0116] In contrast, the inkjet ink composition of Comparative Example 1 had a large average particle size immediately after production, and was unable to achieve inkjet printability as excellent as that of Examples 1 and 2. Furthermore, the inkjet ink composition of Comparative Example 2 was excellent in inkjet printability, but was poor in dispersion stability. [Explanation of symbols]

[0117] 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. preparing a dispersion containing metal oxide nanoparticles and a glycol-based solvent; mixing the dispersion with a non-alcoholic solvent; 1. A method for producing an inkjet ink composition comprising:

2. The method for producing an ink-jet ink composition according to claim 1 , wherein 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.

3. 2. The method for producing an ink-jet ink composition according to claim 1, wherein 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, and titanium oxide.

4. The method for producing an ink-jet ink composition according to claim 1 , wherein the metal oxide nanoparticles include at least one of nanoparticles containing nickel oxide and nanoparticles containing zinc oxide.

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

6. The method for producing an ink-jet ink composition according to claim 1 , wherein the ink-jet ink composition contains the metal oxide nanoparticles at a concentration in the range of 0.05% by mass to 20% by mass.

7. The mass M of the glycol-based solvent Ａ and the mass M of the non-alcoholic solvent Ｂ The mass M of the non-alcoholic solvent in the total Ｂ The ratio M Ｂ / (M Ａ +M Ｂ 2. The method for producing an ink-jet ink composition according to claim 1, wherein the value of (a) is in the range of 0.10 to 0.

50.

8. The method for producing an 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.

9. The method for producing an ink-jet ink composition according to claim 1 , wherein the non-alcoholic solvent is at least one selected from the group consisting of an amide compound, an aliphatic ester compound, and an aliphatic ether compound.

10. An ink-jet ink composition produced by the method of any one of claims 1 to 9.

11. Producing an ink-jet ink composition by the method of any one of claims 1 to 9; supplying the inkjet ink composition to a surface of a substrate by inkjet printing to form a coating film; A method for forming a printing layer comprising:

12. A printing layer formed by the method according to claim 11.

13. A display device comprising the printed layer according to claim 12.

14. A method for manufacturing a display device, comprising forming a print layer by the forming method according to claim 11.

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