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 a substrate by inkjet printing, and the inkjet ink composition used to form the coating film includes 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 coating film is formed under conditions where the contact angle of water with the surface at 25°C is within the range of 10 to 50°.

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, which includes forming a coating film on the surface of a substrate by inkjet printing, wherein the inkjet ink composition used to form the coating film contains 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 under conditions where the contact angle of water with the surface at 25°C is in the range of 10 to 50°.

[0006] According to another aspect of the present invention, there is provided a method for forming a printing layer according to the above aspect, further comprising increasing the surface free energy of the surface prior to forming the coating film.

[0007] According to yet another aspect of the present invention, there is provided a method for forming a printing layer according to the above aspect, in which the surface free energy of the surface is increased by at least one of supplying water to the surface and irradiating the surface with ultraviolet light.

[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, 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.

[0009] 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.

[0010] 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 proportion of the metal oxide nanoparticles in the inkjet ink composition is in the range of 0.1% by mass to 10% by mass.

[0011] 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.

[0012] According to yet another aspect of the present invention, there is provided the method for forming a printing layer according to any one of the above aspects, wherein the proportion of the glycol-based solvent in the dispersion medium is in the range of 50% by mass to 100% by mass.

[0013] 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.

[0014] According to yet another aspect of the present invention, there is provided a method for forming a printing layer according to the above aspect, wherein the non-alcoholic solvent is one or more aprotic solvents such as amide compounds, aliphatic ester compounds, and aliphatic ether compounds.

[0015] According to yet another aspect of the present invention, there is provided a method for forming a printing layer relating to any of the above aspects, wherein the proportion of the non-alcohol-based solvent in the components of the dispersion medium other than the glycol-based solvent is in the range of 80% by mass to 100% by mass.

[0016] 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, in which the coating film is formed by moving an inkjet head relative to the substrate and ejecting the inkjet ink composition from the inkjet head onto the substrate such that landing positions of the inkjet ink composition on the surface form a checkerboard pattern.

[0017] 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 relative movement and the ejection are performed so that first dots made of the inkjet ink composition are formed at positions that constitute odd-numbered columns of the checkerboard pattern among the landing positions, and then second dots made of the inkjet ink composition are formed at positions that constitute even-numbered columns of the checkerboard pattern among the landing positions.

[0018] 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.

[0019] 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.

[0020] 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 forming method according to any one of the above aspects. [Effects of the Invention]

[0021] 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]

[0022] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a display device that can be manufactured by a method 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 schematically showing the printed layer formed in Example 1. [Figure 4] FIG. 4 is a top view schematically showing the printed layer formed in Example 2. [Figure 5] FIG. 5 is a top view schematically showing the printed layer formed in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0023] 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.

[0024] 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.

[0025] 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.

[0026] <1> display device Fig. 1 is a cross-sectional view showing an example of a display device that can be manufactured 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The anode 12 including the light-reflecting layer may further include a light-transmitting layer on the light-reflecting layer. The light-transmitting layer may be made of any of the materials exemplified for the light-transmitting electrode. The material constituting the upper surface of the anode 12 preferably has a large work function.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] <2> Display device manufacturing method The display device 1 shown in FIG. 1 can be manufactured, for example, by the following method.

[0064] First, a structure including a substrate 11, an anode 12, and a partition layer 13 is prepared.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] <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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] According to one example, the surface tension of the ink-jet ink composition at 25° C. is in the range of 20 mN / m to 40 mN / m. Preferably, the surface tension of the ink-jet ink composition at 25° C. is in the range of 25 mN / m to 35 mN / m.

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

[0083] <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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] In manufacturing the display device 1, for example, the inkjet printing device described above is used to form one or more of the hole injection layer 14, the hole transport layer 15, and the electron transport layer 17. Then, a coating film is formed on the surface to be printed by the inkjet printing method under conditions where the contact angle of water with respect to the surface to be printed, i.e., the surface to be printed, is within a predetermined range.

[0092] The contact angle of water with the printing surface at 25° C. is set to be within the range of 10 to 50°, preferably within the range of 15 to 40°, and more preferably within the range of 20 to 35°. When the contact angle is set within this range, a coating film can be formed on the printing surface with high shape and dimensional accuracy, and therefore a printing layer made of this coating film can be formed with high shape and dimensional accuracy.

[0093] 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.

[0094] As described above, the above method allows the printed layer to be formed with a shape and dimensions almost exactly as designed. Furthermore, the printed layer obtained by this method 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 above method, the above-mentioned electric field concentration is unlikely to occur, and the resulting deterioration and brightness unevenness are unlikely to occur. In this way, the technology described here can contribute to improving the performance of light-emitting devices having a layer of metal oxide nanoparticles between the cathode and anode.

[0095] The above-mentioned contact angle can be achieved, for example, by selecting a material having an appropriate surface free energy as the material constituting the printing surface of the substrate. However, the material constituting the printing surface of the substrate is usually selected from other perspectives, such as light transparency and electrical properties such as charge injection and charge transport. The surface free energy of the material selected in this manner is usually below the lower limit of the above range. In such cases, the surface free energy of the printing surface is increased prior to forming a coating film.

[0096] The surface free energy of the printing surface can be increased, for example, by supplying water to the printing surface or by irradiating the printing surface with ultraviolet light. Such treatments result in, for example, water molecules adsorbing onto the printing surface, organic matter being removed from the printing surface, or hydrophilic groups such as OH groups, CHO groups, and COOH groups being generated on the printing surface, or two or more of these. As a result, the surface free energy of the printing surface increases. The increase in surface free energy can be adjusted, for example, by the drying conditions performed after supplying water to the printing surface or the ultraviolet light irradiation conditions, such as the irradiation time.

[0097] The formation of a coating film by the inkjet method is preferably carried out by the following method: That is, the coating film is preferably formed by moving the inkjet head relative to the substrate and ejecting the inkjet ink composition from the inkjet head onto the substrate so that the landing positions of the inkjet ink composition on the substrate form a checkerboard pattern.

[0098] 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.

[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 should land. On the other hand, the second region 22 is an area where the inkjet ink composition does not 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] When the above-described relative movement and ejection are performed as described with reference to FIG. 2, dots formed by the landing of ink droplets spread on the printing surface and coalesce with adjacent dots, ultimately forming a continuous film. In this method, the inkjet ink composition is not deposited in the second region 22, so the printing surface includes uncovered areas not covered with the inkjet ink composition during the period until a continuous film is formed. These uncovered areas suppress excessive flow of the inkjet ink composition. Furthermore, in this method, a relatively long time is required from the start of ejection to the formation of a continuous film, and during this period the inkjet ink composition dries and its viscosity increases. Therefore, by performing the above-described relative movement and ejection so that the landing positions form a checkerboard pattern, a printed layer can be formed with even higher shape and dimensional accuracy.

[0102] When the above-mentioned relative movement and ejection are performed so that the landing positions form a checkerboard pattern, it is preferable that the controller controls the operation of the movement mechanism and the inkjet head so that the following first to fourth steps are performed in order.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] When the landing positions are set as explained with reference to FIG. 2, the droplets are landed in the first to fourth steps as will be explained below.

[0108] In the first and third steps, first dots made of the inkjet ink composition are formed at positions constituting odd-numbered columns of the checkerboard pattern among the landing positions. That is, in the array shown in Figure 2, the landing positions in the first and third steps are the centers of the first regions 21 included in the odd-numbered columns of the first regions 21 extending in the Y direction.

[0109] In the second and fourth steps, second dots made of the inkjet ink composition are formed as the dots at positions constituting even-numbered columns included in the checkerboard pattern among the landing positions. That is, in the array shown in Figure 2, the centers of the first regions 21 included in the even-numbered columns among the columns of first regions 21 extending in the Y direction are defined as landing positions in the second and fourth steps.

[0110] 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, a printing layer is obtained as a continuous film.

[0111] 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.

[0112] 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 surface 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 less likely to move, and these first dots limit the movement of the inkjet ink composition constituting the second dots. Therefore, this method allows the coating film and the printed layer formed by drying it to be formed with even higher shape and dimensional accuracy.

[0113] The third and fourth steps may be omitted. The cycle consisting of the third and fourth steps may be carried out two or more times.

[0114] 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.

[0115] 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]

[0116] The following describes tests carried out in connection with the present invention.

[0117] <Example 1> An ink-jet ink composition was prepared containing metal oxide nanoparticles and a dispersion medium.

[0118] 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.

[0119] 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 %.

[0120] Next, a glass substrate was prepared, with a transparent electrode made of indium tin oxide provided on one main surface. This transparent electrode was washed with pure water and then dried. After washing and drying, the contact angle of pure water with the transparent electrode was 27° at 25°C.

[0121] Next, a printed layer was formed on the washed and dried transparent electrode 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.

[0122] Fig. 3 is a top view schematically showing the printed layer formed in Example 1. As shown in Fig. 3, in this example, the printed layer 30B formed on the transparent electrode, which is the substrate 20, had a shape and dimensions substantially equal to those of the printing region 30A where it was to be formed, i.e., had a shape and dimensions substantially as designed.

[0123] <Example 2> In this example, a printed layer was formed in the same manner as in Example 1, except for the following point: In this example, the washing of the transparent electrode with pure water and the subsequent drying were omitted. The contact angle of pure water on the transparent electrode that had not been washed or dried was 56° at the above temperature.

[0124] Fig. 4 is a top view schematically showing the printed layer formed in Example 2. As shown in Fig. 4, in this example, the printed layer 30B formed on the transparent electrode, which is the substrate 20, was composed of a plurality of dots 30BD that were spaced apart from one another. In other words, in this example, the dots made of the inkjet ink composition could not be united, and the printed layer 30B had a shape and dimensions that were significantly different from the design.

[0125] <Example 3> In this example, a printed layer was formed in the same manner as in Example 1, except for the following points: In this example, the transparent electrode was washed with pure water and then dried, and then the transparent electrode was irradiated with extreme ultraviolet light (wavelength 13.5 nm) at an integrated dose of 300 mJ / cm 2 . 2 The contact angle of pure water on the transparent electrode immediately after irradiation with extreme ultraviolet light was 8° at the above temperature.

[0126] Fig. 5 is a top view schematically showing the printed layer formed in Example 3. As shown in Fig. 5, in this example, the printed layer 30B formed on the transparent electrode, which is the printing substrate 20, spread over an area wider than the printed area 30A. In other words, in this example as well, the printed layer 30B had a shape and dimensions that were significantly different from the design. [Explanation of symbols]

[0127] 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, 30BD...dot, PXB...third sub-pixel, PXG...second sub-pixel, PXR...first sub-pixel.

Claims

1. forming a coating film on the surface of a substrate by inkjet printing; The inkjet ink composition used to form the aforementioned coating film 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. The method for forming a printed layer, wherein the coating film is formed under conditions in which the contact angle of water with the surface at 25°C is in the range of 10 to 50°.

2. 2. The method for forming a printing layer according to claim 1, further comprising increasing the surface free energy of the surface prior to forming the coating film.

3. A method for forming a printed layer according to claim 2, wherein the surface free energy of the surface is increased by supplying water to the surface and irradiating the surface with ultraviolet light.

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

5. 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.

6. The method for forming a printed layer according to claim 1, wherein the proportion of the metal oxide nanoparticles in the inkjet ink composition is in the range of 0.1% by mass to 10% by mass.

7. The method for forming a printed 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, triethylene glycol, and hexylene glycol.

8. The method for forming a printing layer according to claim 1 , wherein the proportion of the glycol-based solvent in the dispersion medium is in the range of 50% by mass to 100% by mass.

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

10. The method for forming a printed layer according to claim 9, wherein the non-alcoholic solvent is one or more aprotic solvents such as amide compounds, aliphatic ester compounds, and aliphatic ether compounds.

11. The method for forming a printing layer according to claim 9 , wherein the proportion of the non-alcohol-based solvent in the components other than the glycol-based solvent in the dispersion medium is in the range of 80% by mass to 100% by mass.

12. A method for forming a printed layer according to claim 1, wherein the relative movement of the inkjet head with respect to the substrate and the ejection of the inkjet ink composition from the inkjet head to the substrate are performed such that the placement positions of the inkjet ink composition on the surface form a checkerboard pattern arrangement, thereby forming the coating film.

13. The method for forming a printed layer according to claim 12, wherein the relative movement and ejection are performed such that first dots made of the inkjet ink composition are formed at positions constituting odd-numbered rows included in the checkerboard pattern among the impact positions, and then second dots made of the inkjet ink composition are formed at positions constituting even-numbered rows included in the checkerboard pattern among the impact positions.

14. The method for forming a print layer according to claim 12, wherein the pitch of the checkerboard pattern is in the range of 10 to 100 μm.

15. The method for forming a print layer according to claim 12, 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.

16. A method for manufacturing a display device, comprising forming the print layer by the method according to any one of claims 1 to 15.

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