Printing layer formation method

Abstract

A technology is provided that can contribute to improving the performance of a light-emitting device that has a layer made of metal oxide nanoparticles between a cathode and an anode. [Solution] A method for forming a printed layer includes moving an inkjet head and a substrate relative to each other and discharging an inkjet ink composition from the inkjet head onto the surface of the substrate so that dots of the inkjet ink composition that have landed on the surface merge with each other, thereby forming a coating film on the surface, the 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 the coating film is formed by discharging the inkjet ink composition to a thickness of 1 mm 2 / s~20mm 2 The process is carried out under conditions of a dynamic viscosity in the range of 1 / s, a surface tension in the range of 15 mN / m to 50 mN / m, and a contact angle with respect to the surface in the range of 5° to 40°.

Description

[Technical Field]

[0001] The present invention relates to a method for forming a print layer. [Background technology]

[0002] Layers between the anode and cathode of organic electroluminescent elements and quantum dot light-emitting diodes, as well as wavelength conversion layers, may be formed by inkjet printing. For example, Patent Document 1 describes forming an electron transport layer by inkjet printing. Patent Document 2 describes forming a hole injection layer, a hole transport layer, and an electron transport layer by inkjet printing. [Prior art documents] [Patent documents]

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

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

[0005] According to one aspect of the present invention, a method for forming a coating film on a surface of a substrate includes relatively moving an inkjet head and a substrate, and ejecting an inkjet ink composition from the inkjet head onto the surface of the substrate so that dots of the inkjet ink composition that have landed on the surface merge with each other, the 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 the coating film is formed by discharging the inkjet ink composition to a thickness of 1 mm 2 / s~20mm 2 The present invention provides a method for forming a printing layer under conditions in which the ink has a dynamic viscosity in the range of 1 / s, a surface tension in the range of 15 mN / m to 50 mN / m, and a contact angle with respect to the surface in the range of 5° to 40°.

[0006] According to another aspect of the present invention, there is provided a method for forming a printing layer according to the above aspect, wherein the metal oxide nanoparticles include one or more selected from the group consisting of multiple types of nanoparticles each containing bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide.

[0007] According to yet another aspect of the present invention, there is provided a method for forming a printing layer according to any of the above aspects, wherein the amount of the metal oxide nanoparticles contained in the inkjet ink composition is in the range of 0.05 to 20% by mass.

[0008] According to yet another aspect of the present invention, there is provided a method for forming a printing layer 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, 1,3-propanediol, triethylene glycol, and hexylene glycol.

[0009] According to yet another aspect of the present invention, there is provided the method for forming a print layer according to any one of the above aspects, wherein the printing substrate is a substrate that is transparent to visible light.

[0010] According to yet another aspect of the present invention, there is provided a printed layer formed by the method according to any of the above aspects.

[0011] According to yet another aspect of the present invention, there is provided a display device including the print layer according to the above aspect.

[0012] 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 method according to the above aspect. [Effects of the Invention]

[0013] 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]

[0014] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a display device including a print layer that can be formed by a method according to one embodiment of the present invention. [Figure 2] FIG. 2 is a top view showing an example of a coating film that can be formed by a method according to one embodiment of the present invention. [Figure 3] FIG. 3 is a top view showing another example of a coating film that can be formed by a method according to one embodiment of the present invention. [Figure 4] FIG. 4 is a top view showing a coating film obtained by a method according to a comparative example. [Figure 5] FIG. 5 is a top view showing a coating film obtained by a method according to another comparative example. [Figure 6] FIG. 6 is a top view showing a coating film obtained by a method according to yet another comparative example. [Figure 7] FIG. 7 is a top view showing a coating film obtained by a method according to yet another comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0015] 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.

[0016] 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.

[0017] 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.

[0018] <1> display device Fig. 1 is a cross-sectional view showing an example of a display device including a printed layer that can be formed by a method 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] The partition wall layer 13 is made of an insulator. 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. The partition wall layer 13 may be omitted.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] According to one example, the light-emitting material is a quantum dot, which is a semiconductor particle having a core-shell structure and a particle size ranging from a few nm to about 10 nm.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] <2> Display device manufacturing method The display device 1 shown in FIG. 1 can be manufactured, for example, by the following method.

[0056] First, a structure including a substrate 11, an anode 12, and a partition layer 13 is prepared.

[0057] 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.

[0058] 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.

[0059] Subsequently, the electron transport layer 17 is formed. The electron transport layer 17 can be formed, for example, by an inkjet printing method using an ink composition containing metal oxide nanoparticles and a dispersion medium.

[0060] 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. The formation of the above layers by inkjet printing will be described in detail later.

[0061] <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.

[0062] Furthermore, if the ink-jet ink composition contains an additive, and if this additive remains in the light-emitting element, the light-emitting element will not achieve the expected light-emitting characteristics. Therefore, it is preferable that the ink-jet ink composition does not contain any additive that may remain in the light-emitting element.

[0063] From these viewpoints, it is preferable that one or more of the hole injection layer 14, the hole transport layer 15, and the electron transport layer 17 are formed using an inkjet ink composition having the composition described below.

[0064] That is, a suitable ink-jet ink composition contains metal oxide nanoparticles and a dispersion medium containing a glycol-based solvent, and preferably does not contain any other components that may remain in the light-emitting element.

[0065] 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.

[0066] 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 and nanoparticles containing zinc oxide, for example, any of these nanoparticles.

[0067] The proportion of metal oxide nanoparticles in the inkjet ink composition is preferably in the range of 0.05 to 20% by mass, more preferably in the range of 0.1 to 10% by mass, even more preferably in the range of 0.5 to 5% by mass, and most preferably in the range of 1.2 to 2.0% by mass. The solids concentration of the inkjet ink composition is also preferably in the range described above for the proportion of metal oxide nanoparticles in the inkjet ink composition.

[0068] If the solids concentration is low, the fluidity of the inkjet ink composition increases, and the fluidity decreases with the drying process, requiring a longer drying time. As a result, deviations from the design of the shape or dimensions of the printed layer, as described below, become greater. If the solids concentration is excessively high, it becomes difficult to stably eject the inkjet ink composition from the inkjet head.

[0069] The dispersion medium contains a glycol-based solvent, which may be, for example, one or more selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, triethylene glycol, and hexylene glycol. 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 of the metal oxide nanoparticles.

[0070] The dispersion medium may further contain other solvents. The proportion of glycol solvents in the dispersion medium is preferably in the range of 50% to 100% by mass, and more preferably in the range of 80% to 100% by mass.

[0071] The other solvents can be used to adjust, for example, the viscosity, surface tension, and contact angle of the ink-jet ink composition. The other solvents are preferably non-alcoholic solvents, more preferably one or more aprotic solvents such as amide compounds, aliphatic ester compounds, and aliphatic ether compounds. The one or more aprotic solvents can include, for example, one or more of N,N'-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and propylene glycol monomethyl ether acetate (PGMEA or PGMAc). The proportion of the non-alcoholic solvent or aprotic solvent in the other solvents is preferably in the range of 80% to 100% by mass, and more preferably 100% by mass.

[0072] The proportion of the dispersion medium in the inkjet ink composition is preferably in the range of 80% to 99% by mass, and more preferably in the range of 85% to 99% by mass.

[0073] <4> Printing layer formation method In the display device 1, one or more of the hole injection layer 14, the hole transport layer 15, and the electron transport layer 17 are printed layers formed by inkjet printing. The method for forming the printed layers will be described below.

[0074] The method for forming a printed layer using the inkjet method involves moving an inkjet head relative to a substrate and ejecting an inkjet ink composition from the inkjet head onto the surface of the substrate so that dots of the inkjet ink composition that have landed on the surface merge with each other, thereby forming a coating film on the surface. The substrate is, for example, a substrate that is transparent to visible light. Here, the substrate is a structure that includes a substrate 11.

[0075] The method for forming a print layer uses an inkjet printing device, which includes a support, an inkjet head, a moving mechanism, an imaging device, and a controller.

[0076] The support removably supports the printing medium. For example, the support removably supports the printing medium so that the printing surface of the printing medium faces upward. The support is movable in a direction perpendicular to the thickness direction of the printing medium it supports. Here, as an example, the support is assumed to be movable in the Y direction.

[0077] The inkjet head is installed so as to face the printing surface of the substrate supported by the support. The inkjet head is movable in the thickness direction of the substrate it supports and in a direction perpendicular to the direction of movement of the support. The inkjet head has a plurality of nozzles on the surface facing the substrate. These nozzles are arranged, for example, in a line. These nozzles may form a plurality of rows. Here, as an example, it is assumed that the inkjet head is movable in the X direction and the nozzles are arranged in a line in the X direction at a constant center-to-center distance D0.

[0078] The movement mechanism moves the inkjet head relative to the support. Here, as an example, the movement mechanism moves the support in the Y direction and the inkjet head in the X direction.

[0079] The imaging device captures an image of an alignment mark provided on a printing medium or the like, and outputs the image information obtained thereby.

[0080] The controller includes a central processing unit (CPU) and a storage device. The controller acquires image information output by the imaging device and obtains relative position information between the inkjet head and the substrate from the image information. The controller also controls the relative movement between the inkjet head and the substrate, as well as the ejection of the inkjet ink composition from the inkjet head. Specifically, the controller controls the operation of the movement mechanism and the inkjet head as follows. That is, the controller controls the operation of the movement mechanism so that the support moves in the Y direction. The controller also controls the operation of the inkjet head so that the inkjet head ejects an appropriate amount of inkjet ink composition when the landing position where the ink droplets of the inkjet ink composition should land is located in front of the nozzle. In one example, the landing position is a position corresponding to a lattice point of a square lattice.

[0081] The distance between the centers of adjacent landing positions is preferably in the range of 10 μm to 150 μm, and more preferably in the range of 20 μm to 90 μm.

[0082] The amount of ink-jet ink composition ejected onto one landing position is preferably in the range of 1 pL to 1000 pL, and more preferably in the range of 20 pL to 500 pL.

[0083] In the method for forming a printing layer using this inkjet printing device, the inkjet ink composition is applied to a printing layer of 1 mm 2 / s~20mm 2 The coating is formed under conditions in which the coating has a dynamic viscosity in the range of 1 / s, a surface tension in the range of 15 mN / m to 50 mN / m, and a contact angle with respect to the surface of the printing substrate in the range of 5° to 40°.

[0084] The coating film is preferably formed under conditions in which the ink-jet ink composition has a surface tension in the range of 20 mN / m to 45 mN / m, and even more preferably under conditions in which the ink-jet ink composition has a surface tension in the range of 25 mN / m to 40 mN / m.

[0085] The coating film is formed by applying the ink-jet ink composition to a thickness of 1 mm. 2 / s~15mm 2 It is preferable to carry out the process under conditions in which the kinematic viscosity is in the range of 2 mm / s. 2 / s~10mm 2 It is more preferable to carry out the process under conditions in which the kinematic viscosity is in the range of / s.

[0086] The coating film is preferably formed under conditions in which the inkjet ink composition has a contact angle with the surface in the range of 10° to 35°, and more preferably under conditions in which the inkjet ink composition has a contact angle with the surface in the range of 20° to 30°.

[0087] <5> effect According to the above-described method, for example, a printed layer made of a cured product of the coating film 30B shown in FIG. 2 or FIG. 3 can be formed.

[0088] Fig. 2 is a top view showing an example of a coating film that can be formed by a method according to one embodiment of the present invention, and Fig. 3 is a top view showing another example of a coating film that can be formed by a method according to one embodiment of the present invention.

[0089] 2 and 3, the area surrounded by a dashed line is a printing area 30A on the surface of the print substrate 20 where a printing layer is to be formed. The coating film 30B shown in Figures 2 and 3 is an example of a coating film obtained when the inkjet head and the print substrate are moved relative to each other and the inkjet ink composition is ejected from the inkjet head onto the surface of the print substrate so that the landing positions of the inkjet ink composition form an array of 5 rows and 5 columns in the printing area 30A. The number of columns and the number of rows formed by the landing positions in the printing area 30A may be two or more.

[0090] The ink-jet ink composition that lands on the printing area 30A forms dots at the landing positions, and each of these dots spreads over the printing area 30A due to the kinetic energy of the ink droplets.

[0091] This inkjet ink composition has a sufficiently small dynamic viscosity and a sufficiently small contact angle with respect to the printing area 30A. Therefore, these dots spread sufficiently and coalesce with each other. Furthermore, this inkjet ink composition has a sufficiently large surface tension. Therefore, the dots spread in an extremely short time. As a result, the coating film made of the inkjet ink composition does not have voids (through holes) and forms a continuous film with a substantially uniform thickness.

[0092] Furthermore, this inkjet ink composition has a sufficiently high dynamic viscosity and a sufficiently high contact angle with respect to the printing area 30A, so that the dots do not expand excessively, and the coating film formed as described above does not suffer from excessive shrinkage, as will be described later.

[0093] Therefore, when the coating film is formed under the above conditions, the shape and dimensions of the coating film as viewed in the thickness direction can be made to substantially match the shape and dimensions of the printing area 30A immediately after the coalescence, and can be maintained for a sufficiently long time after the coalescence. Therefore, by drying this coating film, a printed layer can be obtained whose shape and dimensions as viewed in the thickness direction substantially match the shape and dimensions of the printing area 30A.

[0094] As described above, the above-described method can form a layer of metal oxide nanoparticles with nearly the designed shape and dimensions, and therefore can contribute to improving the performance of light-emitting devices having a layer of metal oxide nanoparticles between a cathode and an anode.

[0095] If the coating is formed under other conditions, it is difficult to form a layer of metal oxide nanoparticles in a shape and size that is nearly identical to the desired shape and size, as will be explained below.

[0096] Figures 4 to 7 are top views showing a coating film obtained by a method according to a comparative example. Figure 5 is a top view showing a coating film obtained by a method according to another comparative example. Figure 6 is a top view showing a coating film obtained by a method according to yet another comparative example. Figure 7 is a top view showing a coating film obtained by a method according to yet another comparative example.

[0097] Increasing the kinematic viscosity of the inkjet ink composition and the contact angle with respect to the printing area 30A makes it difficult for the dots of the inkjet ink composition to spread. Therefore, if the kinematic viscosity and contact angle are too large, even if the dots 30BD of the inkjet ink composition coalesce with each other, the coating film 30B formed by this coalescence will have voids 30BV, as shown in Figure 4. Alternatively, if the kinematic viscosity and contact angle are too large, the dots 30BD of the inkjet ink composition will not coalesce with each other, and the coating film 30B will be a discontinuous film, as shown in Figure 5.

[0098] Furthermore, if the dynamic viscosity and contact angle are too large, shrinkage of the coating film 30B may occur. For example, the coating film 30B may shrink from the state shown in FIG. 4 to the state shown in FIG.

[0099] This shrinkage can occur even when the coating film 30B does not have voids 30BV. For example, if the kinematic viscosity of the inkjet ink composition is sufficiently low and the contact angle with the printed area 30A is too large, the dots may coalesce to form a coating film 30B that does not have voids 30BV. However, such a coating film 30B may shrink, for example, to the state shown in FIG. 7, due to the contact angle being too large. [Example]

[0100] Tests and computer simulations carried out in connection with the present invention will be described below.

[0101] (1) Examination (1.1) Test Example 1 An ink-jet ink composition was prepared containing metal oxide nanoparticles and a dispersion medium.

[0102] The metal oxide nanoparticles used were made of nickel (II) oxide and had an average particle size of 30 nm as measured by dynamic light scattering. The amount of the metal oxide nanoparticles was adjusted so that their proportion in the inkjet ink composition was 1% by mass.

[0103] Ethylene glycol (EG) and diethylene glycol monomethyl ether (DEM) were used as the dispersion medium, and the proportion of ethylene glycol in the dispersion medium and the proportion of diethylene glycol monomethyl ether in the dispersion medium were both 50 mass %.

[0104] The inkjet ink composition has a density of 1100 kg / m 3 This inkjet ink composition had a kinematic viscosity of 11.4 mmHg at 25°C. 2 / s, and the surface tension at 25°C was 31.7 mN / m.

[0105] Next, a coating film was formed on a substrate made of soda-lime glass by the method described above, and the coating film was dried to obtain a printed layer. This coating film was formed using the inkjet ink composition described above. Here, the center-to-center distance between adjacent landing positions in the X direction and the center-to-center distance between adjacent landing positions in the Y direction were both 42 μm. The amount of inkjet ink composition supplied to each landing position was approximately 7 pL. The temperature during coating film formation was 25°C. At this temperature, the contact angle of the inkjet ink composition with the substrate was 60°.

[0106] The printed layer thus obtained was observed under a microscope, and it was found that the printed layer had the same structure as that described with reference to FIG.

[0107] (1.2) Test Example 2 A printed layer was formed in the same manner as in Test Example 1, except for the following points. That is, in this example, prior to forming a coating film, the surface of the substrate was washed with water and dried. As a result, the contact angle of the inkjet ink composition with the substrate at 25°C was set to 30°.

[0108] The printed layer thus obtained was observed under a microscope, and the results showed that the printed layer had the same structure as that described with reference to FIG.

[0109] (1.3) Test Example 3 A printed layer was formed in the same manner as in Test Example 1, except for the following points. That is, in this example, prior to forming a coating film, the surface of the substrate was washed with water, dried, and exposed to extreme ultraviolet light. As a result, the contact angle of the inkjet ink composition with the substrate at 25°C was set to 5°.

[0110] The printed layer thus obtained was observed under a microscope, and the results showed that the printed layer had the same structure as that described with reference to FIG.

[0111] (2) Computer simulation The influence of the physical properties of an inkjet ink composition on the shape and dimensions of a coating film obtained from the inkjet ink composition was investigated by computer simulation as described below.

[0112] For this computer simulation, we used Paticleworks (registered trademark; manufactured by Prometech Software, Inc.), a fluid analysis software that uses the particle method. Here, the particle method models the fluid as a collection of particles.

[0113] In this computer simulation, the center-to-center distance of model particles constituting the fluid was set to 1 μm, and the density of the inkjet ink composition was set to 1100 kg / m 3 The diameter of the ink droplets was 24 μm, the center-to-center distance between adjacent nozzles was 42 μm, the initial velocity of the ink droplets was 10 m / s, and the distance from the nozzle to the substrate was 200 μm.

[0114] (2.1) Confirmation of accuracy of computer simulation The kinematic viscosity and surface tension of the inkjet ink composition were 11.4 mm 2 The contact angles of the ink-jet ink composition with respect to the surface of the substrate were set to 60°, 30°, and 5°, and the shape and dimensions of the coating film were determined by computer simulation for each of these cases. The shapes and dimensions of the coating film determined in this manner were compared with the shapes and dimensions of the printed layers formed in Test Examples 1 to 3. As a result, the shapes and dimensions of the coating film determined by computer simulation were consistent with the shapes and dimensions of the printed layers that were actually formed.

[0115] (2.2) Confirmation of the effect of contact angle on the structure of the coating The kinematic viscosity and surface tension of the inkjet ink composition were 11 mm 2 The contact angles of the inkjet ink composition with the surface of the substrate were set to 5°, 30°, 45°, 60°, and 90°, and the shape and dimensions of the coating film were determined by computer simulation. The structure of the resulting coating film was then evaluated based on the following criteria.

[0116] A: The coating film covered the entire printing area, and there was almost no deviation in shape or dimensions from the design. B: The coating film covered the entire printed area, but the deviation from the design in shape and dimensions was relatively large. C: At least part of the printed area was not covered with a coating. The results are shown in Table 1 below.

[0117] [Table 1]

[0118] As shown in Table 1, when the contact angle was small enough, the entire printing area could be covered with the coating film.

[0119] (2.3) Confirmation of the effect of dynamic viscosity on the structure of the coating The surface tension of the ink-jet ink composition and the contact angle with the surface of the printing substrate were set to 31 mN / m and 45°, respectively, and the kinematic viscosity of the ink-jet ink composition was set to 2 mm 2 / s, 5mm 2 / s, 11mm 2 / s, and 20 mm 2 The shape and dimensions of the coating film were determined by computer simulation for each of the cases where the ink jet ink composition was set to a surface tension of 31 mN / m and a contact angle with respect to the surface of a substrate to be printed, respectively. 2 / s, 5mm 2 / s, and 11mm 2 For each of the cases where the thickness was 1 / s, the shape and dimensions of the coating film were determined by computer simulation. The resulting coating film structure was then evaluated based on the following criteria.

[0120] A: The coating film covered the entire printing area, and there was almost no deviation in shape or dimensions from the design. B: The coating had voids but extended to the edge of the printed area, or the coating was continuous but had smaller dimensions than the printed area. C: The coating had a structure of dots spaced apart from each other, or the coating had voids and smaller dimensions than the printed areas. The results are shown in Table 2 below.

[0121] [Table 2]

[0122] As shown in Table 2, when the kinematic viscosity was decreased, adjacent dots were connected. Furthermore, the coating film obtained by connecting adjacent dots had smaller dimensions when the contact angle was large than when the contact angle was small.

[0123] (2.4) Confirmation of the effect of surface tension on the structure of the coating The kinematic viscosity of the ink-jet ink composition and the contact angle with the surface of the substrate were measured at 11 mm 2 The kinematic viscosity of the ink-jet ink composition and the contact angle with the surface of the substrate were set to 11 mm / s and 30°, and the surface tension of the ink-jet ink composition was set to 31 mN / m and 50 mN / m, respectively. 2 The angle was set to 3 / s and 45°, and the surface tension of the ink-jet ink composition was set to 31 mN / m and 50 mN / m. The shape and dimensions of the coating film were calculated by computer simulation. The structure of the resulting coating film was then evaluated based on the following criteria.

[0124] A: The coating film covered the entire printing area, and there was almost no deviation in shape or dimensions from the design. B: The coating film covered the entire printed area, but the deviation from the design in shape and dimensions was relatively large. C: At least part of the printed area was not covered with a coating.

[0125] The results are shown in Table 3 below. Table 3 also shows the time required from the impact of the ink droplets on the surface of the printing substrate until the structure of the coating film becomes stable.

[0126] [Table 3]

[0127] As shown in Table 3, when the surface tension was high, the structure of the coating film stabilized in a shorter time than when the surface tension was low. [Explanation of symbols]

[0128] 1...display device, 11...substrate, 12...anode, 13...barrier layer, 14...hole injection layer, 15...hole transport layer, 16...light-emitting layer, 17...electron transport layer, 18...cathode, 20...printed body, 30A...printed area, 30B...coating film, 30BD...dot, 30BV...void, PXB...third sub-pixel, PXG...second sub-pixel, PXR...first sub-pixel.

Claims

1. a method for producing a coating film on a surface of a substrate by relatively moving an inkjet head and the substrate and discharging an inkjet ink composition from the inkjet head onto the surface of the substrate so that dots of the inkjet ink composition that have landed on the surface merge with each other, The inkjet ink composition comprises metal oxide nanoparticles made of a material selected from the group consisting of a hole injection material, a hole transport material, and an electron transport material, and a dispersion medium containing a glycol-based solvent; The coating film is formed by applying the inkjet ink composition to a substrate of 1 mm ２ / s to 20mm ２ A method for forming a printing layer under conditions in which the ink has a dynamic viscosity in the range of 1000 kJ / s, a surface tension in the range of 15 mN / m to 50 mN / m, and a contact angle with respect to the surface in the range of 5° to 40°.

2. 2. The method for forming a printing layer according to claim 1, wherein the metal oxide nanoparticles include one or more selected from the group consisting of multiple types of nanoparticles each containing bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide.

3. The method for forming a printing layer according to claim 1 , wherein the amount of the metal oxide nanoparticles contained in the inkjet ink composition is in the range of 0.05 to 20% by mass.

4. The method for forming a printing layer according to claim 1, wherein the glycol-based solvent is one or more selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, triethylene glycol, and hexylene glycol.

5. The method for forming a print layer according to claim 1, wherein the printing medium is a substrate that is transparent to visible light.

6. A printed layer formed by the method according to any one of claims 1 to 5.

7. A display device comprising the printed layer according to claim 6.

8. A method for manufacturing a display device, comprising forming a print layer by the method according to any one of claims 1 to 5.

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