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 forming a coating film on the surface of the substrate by performing relative movement between an inkjet head and a substrate and ejecting an inkjet ink composition from the inkjet head, wherein the inkjet ink composition comprises metal oxide nanoparticles made of a material selected from the group consisting of hole injection materials, hole transport materials, and electron transport materials, and a dispersion medium containing a glycol-based solvent, and the relative movement and ejection are performed such that the landing positions of the inkjet ink composition on the surface form a checkerboard pattern and the dots made of the inkjet ink composition that have landed on the surface merge with each other.

Description

[Technical Field]

[0001] The present invention relates to the formation of a printed layer. [Background technology]

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

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

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

[0005] According to one aspect of the present invention, there is provided a method for forming a printed layer, comprising: forming a coating film on the surface of a substrate by performing relative movement between an inkjet head and a substrate and ejecting an inkjet ink composition from the inkjet head, wherein 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, and the relative movement and ejection are performed such that landing positions of the inkjet ink composition on the surface form a checkerboard pattern arrangement and dots made of the inkjet ink composition that have landed on the surface merge with one another.

[0006] According to another aspect of the present invention, there is provided a method for forming a printing layer relating to the above aspect, in which the relative movement and the ejection are performed so that first dots are formed as the dots at positions that constitute odd-numbered columns of the checkerboard pattern arrangement among the impact positions, and then second dots are formed as the dots at positions that constitute even-numbered columns of the checkerboard pattern arrangement among the impact positions.

[0007] According to yet another aspect of the present invention, there is provided the method for forming a printed layer according to any of the above aspects, wherein the relative movement and the discharge are performed so as to form a continuous film as the coating film.

[0008] According to yet another aspect of the present invention, there is provided a method for forming a printed layer according to any of the above aspects, further comprising supplying a second ink composition containing the same solid content as the solid content contained in the inkjet ink composition onto the coating film.

[0009] According to yet another aspect of the present invention, there is provided the method for forming a printed layer according to any one of the above aspects, wherein the pitch of the checkerboard pattern is within a range of 10 to 100 μm.

[0010] According to yet another aspect of the present invention, there is provided the method for forming a printed layer according to any of the above aspects, wherein the amount of the ink-jet ink composition supplied to each of the landing positions is within the range of 1 to 20 pL.

[0011] According to yet another aspect of the present invention, there is provided the method for forming a printed layer according to any one of the above aspects, wherein the ink-jet ink composition has a solids concentration in the range of 1.2 to 2.0% by mass.

[0012] According to yet another aspect of the present invention, there is provided the method for forming a printed layer according to any one of the above aspects, wherein the dispersion medium further contains a non-alcoholic solvent.

[0013] According to yet another aspect of the present invention, there is provided a method for forming a printed layer according to any of the above aspects, wherein the metal oxide nanoparticles include one or more of a plurality of types of nanoparticles, each of which contains bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, molybdenum oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide.

[0014] 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 metal oxide nanoparticles include at least one of nanoparticles containing nickel oxide and nanoparticles containing zinc oxide.

[0015] According to yet another aspect of the present invention, there is provided the method for forming a printed layer according to any of the above aspects, wherein the metal oxide nanoparticles have an average particle diameter in the range of 3 nm to 50 nm as measured by dynamic light scattering.

[0016] 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, triethylene glycol, and hexylene glycol.

[0017] According to yet another aspect of the present invention, there is provided a method for manufacturing a display device, the method including forming the print layer by the method according to any one of the above aspects.

[0018] 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.

[0019] According to yet another aspect of the present invention, there is provided a display device including the print layer according to the above aspect.

[0020] According to yet another aspect of the present invention, there is provided a printing layer 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 having a corrugated surface in a cross section parallel to the thickness direction.

[0021] According to yet another aspect of the present invention, there is provided a display device including the print layer according to the above aspect. [Effects of the Invention]

[0022] 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]

[0023] [Figure 1] FIG. 1 is a cross-sectional view of a display device according to one embodiment of the present invention. [Figure 2] FIG. 2 is a top view showing an arrangement of landing positions in a method for forming a print layer according to one embodiment of the present invention. [Figure 3] FIG. 3 is a top view showing a printed layer according to one embodiment of the present invention. [Figure 4] FIG. 4 is a top view showing the arrangement of landing positions in the printing layer forming methods according to the first and second comparative examples. [Figure 5] FIG. 5 is a top view showing printed layers according to the first and second comparative examples. [Figure 6]FIG. 6 is a cross-sectional view showing a printing layer according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] 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.

[0025] 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.

[0026] 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.

[0027] <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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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 size of these metal oxide nanoparticles, measured by dynamic light scattering, is preferably within the range described above for the hole injection material.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] <2> Display device manufacturing method The display device 1 shown in FIG. 1 can be manufactured, for example, by the following method.

[0065] First, a structure including a substrate 11, an anode 12, and a partition layer 13 is prepared.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] <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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] Preferably, the metal oxide nanoparticles include one or more of a plurality of types of nanoparticles each containing bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, molybdenum oxide, nickel oxide, zinc oxide, and titanium oxide, for example, any of these nanoparticles. More preferably, the metal oxide nanoparticles include at least one of nanoparticles containing nickel oxide and nanoparticles containing zinc oxide, for example, any one of these nanoparticles.

[0076] The proportion of metal oxide nanoparticles in the inkjet ink composition is preferably in the range of 0.1 to 10% by mass, more preferably in the range of 0.5 to 5% by mass, and even more 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.

[0077] 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.

[0078] The dispersion medium contains a glycol-based solvent. 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 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.

[0079] 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.

[0080] The other solvents can be used, for example, to adjust the surface tension and viscosity 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.

[0081] 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.

[0082] According to one example, the ink-jet ink composition has a surface tension in the range of 20 mN / m to 40 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.

[0083] In addition, the ink-jet ink composition has a viscosity at 25° C. of, for example, 20 mPa·s or less.

[0084] <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.

[0085] In the method for forming a printed layer using the inkjet method, a coating film is formed on the surface of a substrate by moving an inkjet head relative to the substrate and ejecting an inkjet ink composition from the inkjet head. Here, the substrate is a structure including a substrate 11.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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 and the ejection of the inkjet ink composition from the inkjet head.

[0092] Here, the controller controls the operation of the moving mechanism and the inkjet head so that the following first to fourth steps are carried out in order.

[0093] In the first step, the controller controls the operation of the movement mechanism to move the support in the Y direction. The controller also controls the operation of the inkjet head so that the inkjet head ejects an appropriate amount of the inkjet ink composition when the landing position of the ink droplets of the inkjet ink composition is located in front of the nozzle. Then, when the area facing the nozzle of the inkjet head changes from near a first end of the printing surface of the printing medium to near a second end of the printing surface, the controller controls the operation of the movement mechanism to stop the movement of the support in the Y direction, and controls the operation of the inkjet head to stop ejecting the inkjet ink composition.

[0094] In the second step, the controller controls the operation of the movement mechanism so that the inkjet head moves in the X direction by half the center-to-center distance D0 of the nozzles. Next, the controller controls the operation of the movement mechanism so that the support moves in the opposite direction 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 impact position is positioned directly in front of the nozzles. Then, when the area facing the nozzles of the inkjet head changes from near the second edge of the printing surface of the printing medium to near the first edge of the printing surface, the controller controls the operation of the movement mechanism so that the movement of the support in the Y direction stops, and controls the operation of the inkjet head so that the ejection of the inkjet ink composition stops.

[0095] In the third step, the controller controls the operation of the movement mechanism so that the inkjet head moves a predetermined distance in the X direction. Here, the predetermined distance is the sum D+D0 of the center-to-center distance D from the nozzle at one end to the nozzle at the other end and the center-to-center distance D0 between adjacent nozzles. Next, the controller controls the operation of the movement mechanism so that the support moves in the Y direction in the same direction as in the first step. 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 impact position is positioned directly in front of the nozzle. Then, when the area facing the nozzle of the inkjet head changes from near the first end of the printing surface of the printing medium to near the second end of the printing surface, the controller controls the operation of the movement mechanism so that the movement of the support in the Y direction stops, and controls the operation of the inkjet head so that the ejection of the inkjet ink composition stops.

[0096] In the fourth step, the controller controls the operation of the movement mechanism so that the inkjet head moves in the X direction by half the center-to-center distance D0 of the nozzles. Next, the controller controls the operation of the movement mechanism so that the support moves in the opposite direction 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 impact position is positioned directly in front of the nozzles. Then, when the area facing the nozzles of the inkjet head changes from near the second edge of the printing surface of the printing medium to near the first edge of the printing surface, the controller controls the operation of the movement mechanism so that the movement of the support in the Y direction stops, and controls the operation of the inkjet head so that the ejection of the inkjet ink composition stops.

[0097] Steps 3 and 4 may be omitted. In addition, a cycle consisting of steps 3 and 4 may be carried out two or more times.

[0098] Fig. 2 is a top view showing an arrangement of landing positions in a method for forming a printed layer according to one embodiment of the present invention, and Fig. 3 is a top view showing a printed layer according to one embodiment of the present invention.

[0099] The printing surface of the print substrate 20 shown in Figure 2 includes a first region 21 and a second region 22. The center of the first region 21 is the landing position where the inkjet ink composition is to land. On the other hand, the second region 22 is an area where the inkjet ink composition is not to land. Note that the boundary between the first region 21 and the second region 22 is drawn for ease of understanding and does not exist on the actual printing surface.

[0100] The first regions 21 and the second regions 22 are arranged alternately in the X direction and the Y direction in each through-hole provided in the partition layer 13. That is, the first regions 21 form a checkerboard arrangement, and therefore the landing positions also form a checkerboard arrangement.

[0101] In manufacturing the display device 1, when forming one or more of the hole injection layer 14, the hole transport layer 15, and the electron transport layer 17, for example, the inkjet method described above is used, and the landing position is set as described with reference to Figure 2.

[0102] More specifically, in the first and third steps, the first dots are formed at positions constituting odd-numbered columns in the checkerboard pattern. That is, in the array shown in Fig. 2, the centers of the first regions 21 included in the odd-numbered columns of the columns of first regions 21 extending in the Y direction are set as the landing positions in the first and third steps.

[0103] In the second and fourth steps, second dots are formed at positions that constitute even-numbered columns in the checkerboard pattern. That is, in the array shown in Fig. 2, the centers of the first regions 21 included in the even-numbered columns of the first regions 21 extending in the Y direction are set as the landing positions in the second and fourth steps.

[0104] Then, the dots of the inkjet ink composition that have landed on the printing surface are merged with each other. That is, by forming the second dots in the second step, the first dots formed in the first step and the second dots formed in the second step are merged. Furthermore, by forming the second dots in the fourth step, the first dots formed in the third step and the second dots formed in the fourth step are merged. In this way, the printed layer 30B shown in FIG. 3 is obtained.

[0105] In this method, in each of the first and third steps, first dots adjacent to each other in the X direction are spaced apart from each other, and first dots adjacent to each other in the Y direction are also spaced apart from each other. The first dots formed in the first and third steps do not merge with each other before forming second dots in the second and fourth steps, respectively.

[0106] Immediately before the second dots are formed, the inkjet ink composition constituting the first dots has dried to a certain extent at least on the surfaces of the dots. Therefore, when the first dots and the second dots are merged by forming the second dots, the inkjet ink composition constituting the first dots is unlikely to move, and these first dots limit the movement of the inkjet ink composition constituting the second dots. Therefore, as shown in Figure 3, the coating film obtained by this method and the printed layer 30B obtained by drying it can have a shape and dimensions substantially identical to the printed area 30A where the printed layer is to be formed, i.e., a shape and dimensions substantially as designed.

[0107] Fig. 4 is a top view showing an arrangement of landing positions in the method of forming the printed layer according to the first and second comparative examples, and Fig. 5 is a top view showing the printed layer according to the first and second comparative examples.

[0108] 4, in the method according to the first comparative example, the entire printing surface of the printing medium 20 is made up of the first region 21. In the method according to the first comparative example, the printing layer 30B is formed in the same manner as in the above embodiment, except that the movement distance of the inkjet head in the second and fourth steps is changed from 1 / 2 the distance D0 to the sum of the distance D and the distance D0 (D+D0).

[0109] In this method, when an amount of inkjet ink composition sufficient to cause the first dots and the second dots to coalesce is supplied to each landing position, the dots formed by the landing of the ink droplets coalesce with the previously formed dots or with the film formed by the coalescence of the dots immediately after landing. This coalescence causes the inkjet ink composition to flow, which prevents the inkjet ink composition from drying on the surface of the film. Therefore, the film maintains a high fluidity for a relatively long time, and the surface energy of the printing surface and the surface tension of the inkjet ink composition can have a significant effect on its shape and dimensions. Therefore, the printed layer 30B obtained by this method may have a shape or dimensions that are significantly different from the shape or dimensions of the printing area 30A where the printed layer is to be formed, i.e., a shape or dimensions that are significantly different from the design, as shown in FIG. 5 .

[0110] 4, in the method according to the second comparative example, the entire printing surface of the printing medium 20 is made up of the first region 21. Except for this, in the method according to the second comparative example, the printing layer 30B is formed in the same manner as in the above embodiment.

[0111] In this method, when a sufficient amount of inkjet ink composition is supplied to each landing position to cause the first dots and second dots to coalesce, the first dots coalesce in each of the first and third steps. The coalescence of these first dots causes the inkjet ink composition to flow, which prevents the inkjet ink composition from drying on the surface of the film. Therefore, when the second dots and the film coalesce as a result of forming the second dots, the inkjet ink composition constituting the film formed by the coalescence of the first dots is likely to move, and the inkjet ink composition constituting the second dots is also likely to move. Therefore, as shown in FIG. 5, the printed layer 30B obtained by this method may have a shape or dimensions significantly different from those of the printing region 30A where the printed layer is to be formed, i.e., a shape or dimensions significantly deviating from the design.

[0112] 1, if one or more of the layers contained in the light-emitting element have a shape or size that is significantly different from the design, deterioration and brightness unevenness due to electric field concentration may occur. Furthermore, if the central portion of one or more layers contained in the light-emitting element is thicker than the peripheral portion, or if the peripheral portion is thicker than the peripheral portion, deterioration and brightness unevenness due to electric field concentration may also occur.

[0113] As described above, the method described with reference to FIG. 2 allows the printed layer 30B to be formed with a shape and dimensions nearly consistent with the design. Furthermore, the printed layer 30B obtained by the method described with reference to FIG. 2 can have a relatively uniform thickness. Therefore, when manufacturing a display device 1 in which one or more of the hole injection layer 14, hole transport layer 15, and electron transport layer 17 are formed by the method described with reference to FIG. 2, the electric field concentration described above is unlikely to occur, and the resulting deterioration and brightness unevenness are unlikely to occur. Thus, the technique described with reference to FIG. 2 can contribute to improving the performance of light-emitting devices having a layer of metal oxide nanoparticles between a cathode and an anode.

[0114] The printed layer 30B obtained by the method described with reference to FIG. 2 has a relatively uniform thickness throughout, but may have irregularities on the surface, as will be described below.

[0115] 6 is a cross-sectional view showing a printed layer according to one embodiment of the present invention, illustrating an example of a printed layer 30B obtained by the method described with reference to FIG.

[0116] The printed layer 30B has a corrugated surface in a cross section parallel to its thickness direction. The printed layer 30B has protrusions 30P and recesses 30R on its surface. According to one example, the protrusions 30P are arranged in islands corresponding to the first dots, and the recesses 30R are square lattice-shaped portions including portions corresponding to the second dots. According to another example, the protrusions 30P are square lattice-shaped portions including portions corresponding to the first dots, and the recesses 30R are arranged in islands corresponding to the second dots.

[0117] 2, as described above, the first dots are dried to a certain extent, and then the second dots are formed and merged together. Therefore, the printed layer 30B obtained by this method may have a greater thickness at the positions of the first dots, or at the positions of the first dots and their vicinity, than at other positions.

[0118] In FIG. 6, for ease of understanding, the thickness T P and the thickness T at the position of the recess 30R. R The difference between T P -T R Although it is drawn larger, this difference T P -T R is actually small.

[0119] difference T P -T R is, for example, 100 nm or less, typically 50 nm or less. P -T R The lower limit of is zero, but the difference T P -TR is, for example, 30 nm or more, the convex portions 30P and concave portions 30R can be easily confirmed.

[0120] 2, the relative movement between the inkjet head and the substrate and the ejection of the inkjet ink composition from the inkjet head are performed so as to form a continuous film as the coating film. These relative movement and ejection may also be performed so as to form a film with openings at the positions of the second regions 22 as the coating film.

[0121] When a film having openings at the positions of the second regions 22 is formed as the coating film, it is preferable to supply a second ink composition containing the same solid content as the solid content of the inkjet ink composition onto the coating film. This makes it possible to seal the openings in the previously formed coating film. The second ink composition is preferably supplied by inkjet printing, but other printing methods may also be used. The second ink composition may also be supplied to a coating film that does not have openings. The pitch of the checkerboard pattern described with reference to FIG. 2 is preferably in the range of 1 to 100 μm, and more preferably in the range of 20 to 50 μm.

[0122] The amount of ink-jet ink composition supplied to each landing position is preferably in the range of 1 to 100 pL, and more preferably in the range of 1 to 60 pL. [Example]

[0123] The following describes tests carried out in connection with the present invention.

[0124] <Example 1> An ink-jet ink composition was prepared containing metal oxide nanoparticles and a dispersion medium.

[0125] 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.

[0126] 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 %.

[0127] Next, a printed layer was formed on a substrate made of soda-lime glass by the method described with reference to FIG. 2. This printed layer 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 7 pL.

[0128] The printed layer thus obtained had a thickness of approximately 30 nm over almost the entire surface, and had a shape and dimensions almost as designed.

[0129] <Example 2> In this example, a printed layer was formed using the same method as in Example 1, except for the following points: That is, in this example, the method according to the second comparative example described above with reference to Fig. 4 was adopted. 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 21 µm.

[0130] The printed layer obtained in this manner had a large variation in thickness compared to the printed layer obtained in Example 1. Furthermore, this printed layer had a shape and dimensions that were significantly different from the design. [Explanation of symbols]

[0131] 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, 20...printed body, 21...first region, 22...second region, 30A...printed region, 30B...printed layer, 30P...protruding portion, 30R...recessed portion, 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, 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 method for forming a printed layer includes the steps of: moving the ink jet ink composition relative to the surface; ejecting the ink jet ink composition so that the landing positions of the ink jet ink composition on the surface form a checkerboard pattern; and merging the dots of the ink jet ink composition that have landed on the surface with each other.

2. 2. The method for forming a printing layer according to claim 1, wherein the relative movement and the ejection are performed so that first dots are formed at positions that constitute odd-numbered columns of the checkerboard pattern among the impact positions, and then second dots are formed at positions that constitute even-numbered columns of the checkerboard pattern among the impact positions.

3. The method for forming a printing layer according to claim 1 , wherein the relative movement and the ejection are performed so as to form a continuous film as the coating film.

4. The method for forming a printing layer according to claim 1 , further comprising supplying a second ink composition containing the same solid content as that of the ink-jet ink composition onto the coating film.

5. 2. The method for forming a print layer according to claim 1, wherein the pitch of the checkerboard pattern is in the range of 10 to 100 [mu]m.

6. The method for forming a print layer according to claim 1 , wherein the amount of the ink-jet ink composition supplied to each of the landing positions is within a range of 1 to 20 pL.

7. The method for forming a printed layer according to claim 1 , wherein the ink-jet ink composition has a solids concentration in the range of 1.2 to 2.0% by mass.

8. The method for forming a printing layer according to claim 1 , wherein the dispersion medium further contains a non-alcoholic solvent.

9. The method for forming a printing layer according to claim 1, wherein the metal oxide nanoparticles include one or more of a plurality of types of nanoparticles, each of which contains bismuth oxide, cobalt oxide, copper oxide, magnesium oxide, molybdenum oxide, nickel oxide, zinc oxide, magnesium-doped zinc oxide, and titanium oxide.

10. The method for forming a printing layer according to claim 1 , wherein the metal oxide nanoparticles include at least one of nanoparticles containing nickel oxide and nanoparticles containing zinc oxide.

11. The method for forming a printing layer 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.

12. The method for forming a printing layer 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.

13. A method for manufacturing a display device, comprising forming the printed layer by the method according to any one of claims 1 to 12.

14. A printed layer formed by the method of any one of claims 1 to 12.

15. A display device comprising the printed layer according to claim 14.

16. A printing layer 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 having a corrugated surface in a cross section parallel to the thickness direction.

17. A display device comprising the printed layer according to claim 16.

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