Exposure head and image-forming apparatus

Abstract

To provide an exposure head that can efficiently generate electric charge in a photoreceptor through exposure by an exposure head using an organic light emitting element.SOLUTION: An exposure head includes an organic light emitting element, wherein the organic light emitting element includes a first electrode, a second electrode, an organic compound layer disposed between the first electrode and the second electrode, and a protection layer covering the second electrode, wherein the organic compound layer includes a light emitting layer, and the number of peaks in an exposure spectrum 41 emitted from the exposure head is greater than the number of peaks in a PL spectrum 40 of a light emitting material included in the light emitting layer.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an exposure head and an image forming apparatus. [Background technology]

[0002] Photosensitive drums (hereinafter also referred to as "drum-shaped electrophotographic photosensitive members" or "photosensitive members") used in electrophotographic image forming devices are widely used in copiers, facsimile machines, and printers. Such electrophotographic devices are image forming devices equipped with an exposure head (print head) and include a plurality of light-emitting elements. The light-emitting elements include those that use LEDs (Light Emitting Diodes) and those that use organic light-emitting elements (OLEDs). The photosensitive drum is exposed to light emitted from these multiple light-emitting elements, and an image corresponding to the latent image formed on the photosensitive drum is printed on recording paper. Patent Document 1 discloses an exposure head that uses organic light-emitting elements. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2022-100479 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the exposure head described in Patent Document 1 uses a bottom emission structure, and further improvement in efficiency is required. An object of the present invention is to provide an exposure head and an image forming apparatus that can efficiently generate charges on a photosensitive member due to exposure by an exposure head that uses organic light-emitting elements. [Means for solving the problem]

[0005] The exposure head of the present invention is an exposure head having an organic light-emitting element, the organic light-emitting element includes a first electrode, a second electrode, an organic compound layer disposed between the first electrode and the second electrode, and a protective layer covering the second electrode; the organic compound layer has a light-emitting layer, The number of peaks in the exposure spectrum emitted from the exposure head is greater than the number of peaks in the PL spectrum of the luminescent material contained in the luminescent layer. [Effects of the Invention]

[0006] According to the present invention, charges can be generated efficiently on the photoreceptor. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram illustrating an example of an image forming apparatus according to the present invention. [Figure 2] FIG. 10 is a diagram illustrating another example of an image forming apparatus according to the present invention. [Figure 3] FIG. 2 is a longitudinal cross-sectional view illustrating an example of the structure of an organic light-emitting element. [Figure 4] FIG. 10 is a diagram showing an example of a spectrum of an exposure head according to the present invention. [Figure 5] FIG. 10 is a schematic diagram showing one form of a light-emitting device that can be used in the exposure head of the present embodiment. [Figure 6] 1A is a schematic perspective view of a head substrate, FIG. 1B is a diagram showing an arrangement of a plurality of light-emitting elements provided on the head substrate, and FIG. 1C is an enlarged view of a part of FIG. 1B. [Figure 7] 1 is a diagram illustrating an example of a layer structure of a photoreceptor according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] The image forming apparatus of the present invention has a photosensitive member (photosensitive drum) and an exposure head (print head) that exposes the photosensitive member. The exposure head of the present invention has an organic light-emitting element (OLED: Organic Light Emitting Diode).

[0009] FIG. 1 shows an example of an image forming apparatus of the present invention. FIG. 1(a) is a schematic diagram showing an example of an image forming apparatus according to one embodiment of the present invention. The image forming apparatus 400 is an electrophotographic image forming apparatus and includes a photoconductor 27, an exposure head 28, a charging unit 30, a developing unit 31, a transfer unit 32, a transport roller 33, and a fixing unit 35. Light 29 is irradiated from the exposure head 28, and an electrostatic latent image is formed on the surface of the photoconductor 27. The exposure head 28 includes an organic light-emitting element. The developing unit 31 includes toner and the like. The charging unit 30 charges the photoconductor 27. The transfer unit 32 transfers the developed image to a recording medium 34. The transport roller 33 transports the recording medium 34. The recording medium 34 is, for example, paper. The fixing unit 35 fixes the image formed on the recording medium 34.

[0010] 1(b) and 1(c) are diagrams showing the exposure head 28 and are schematic diagrams illustrating a state in which multiple light-emitting units 36 are arranged on a long substrate. Arrow 37 indicates the direction parallel to the axis of the photoconductor, the column direction in which the organic light-emitting elements are arranged. This column direction is the same as the axis direction about which the photoconductor 27 rotates. This direction can also be referred to as the long axis direction of the photoconductor 27. FIG. 1(b) shows a configuration in which the light-emitting units 36 are arranged along the long axis direction of the photoconductor 27. FIG. 1(c) shows a configuration different from FIG. 1(b), in which the light-emitting units 36 are arranged alternately in the column direction in the first and second columns. The first and second columns are arranged at different positions in the row direction. In the first column, multiple light-emitting units 36 are arranged at intervals. In the second column, light-emitting units 36 are located at positions corresponding to the intervals between the light-emitting units 36 in the first column. In other words, multiple light-emitting units 36 are also arranged at intervals in the row direction. The arrangement in FIG. 1(c) can also be described as a grid-like arrangement, a houndstooth arrangement, or a checkerboard pattern.

[0011] Another example of the image forming apparatus of the present invention is shown in Figure 2. Figure 2 is a diagram showing the overall configuration of the apparatus. This image forming apparatus is a digital photography type image forming apparatus, and is composed of a scanner unit 100, an image creating unit 103, a fixing unit 104, a paper feed / transport unit 105, and a printer control unit (not shown) that controls these units.

[0012] The scanner unit 100 illuminates a document placed on a platen, optically reads the document image, and converts the image into an electrical signal to create image data. The image-creating unit 103 rotates and drives the photosensitive drum 102, which is charged by a charger 107. The exposure head 106 (in the figure, 106a, b, c, and d indicate the arrangement of four exposure heads for full-color printing) emits light according to the image data, and the light emitted from the chip surfaces of the arrayed light-emitting element group is focused onto the photosensitive drum 102 by a rod lens array to form an electrostatic latent image. The developer 108 develops the electrostatic latent image formed on the photosensitive drum 102 with toner. The developed toner image is transferred onto paper transported on a transfer belt 111. The image forming unit 103 has four imaging units that perform a series of electrophotographic processes (charging, exposure, development, and transfer). These units are arranged in the order of cyan (C), magenta (M), yellow (Y), and black (K) to form a full-color image. After a predetermined time has elapsed since the start of image formation at the cyan station, the four imaging units sequentially perform image formation operations for magenta, yellow, and black. The paper feed / transport unit 105 feeds paper from a pre-selected paper feed unit among internal paper feed units 109a and 109b, external paper feed unit 109c, and manual paper feed unit 109d. The fed paper is transported to registration rollers 110. The registration rollers 110 transport the paper onto a transfer belt 111 at the timing when the toner image formed by the image forming unit 103 is transferred onto the paper. An optical sensor 113 is disposed opposite the transfer belt 111, and detects the position of a test chart printed on the transfer belt 111 to derive the amount of color misregistration between each station. The amount of color misregistration derived here is notified to an image controller (not shown), which corrects the image position of each color. This control ensures that a full-color toner image is transferred onto the paper without color misregistration. The fixing unit 104 is composed of a combination of rollers and has a built-in heat source such as a halogen heater. It uses heat and pressure to melt and fix the toner on the paper onto which the toner image has been transferred from the transfer belt 111, and the paper is then discharged outside the image forming apparatus by paper discharge rollers 112.

[0013] The printer control unit (not shown) communicates with the MFP control unit (not shown) that controls the entire MFP, and executes control in accordance with its instructions, while managing the status of each unit, including the scanner unit 100, the image creation unit 103, the fixing unit 104, and the paper feed / transport unit 105, and issuing instructions to ensure that the entire unit operates smoothly and in harmony.

[0014] <Exposure head> An example of the configuration of an exposure head adapted to the image forming apparatus according to this embodiment will be described. The image forming apparatus includes a photosensitive element and an exposure head as part of its configuration. The photosensitive element and the exposure head are arranged facing each other. This exposure head is formed from a plurality of organic light-emitting elements and a lens array. The exposure head may include a plurality of light-emitting element rows, or a single light-emitting element row.

[0015] <Organic light-emitting element> The organic light-emitting element has a first electrode, a second electrode, an organic compound layer disposed between the first electrode and the second electrode, and a protective layer covering the second electrode, the organic compound layer having a light-emitting layer. The organic compound layer may further have a first organic compound layer positioned between the first electrode and the light-emitting layer, and a second organic compound layer positioned between the light-emitting layer and the second electrode. In this case, it is preferable that the first electrode is a reflective electrode, the second electrode is a light-extraction electrode, and the thickness of the first organic compound layer is smaller than the thickness of the second organic compound layer.

[0016] FIG. 3 is a longitudinal cross-sectional view illustrating an example of the structure of an organic light-emitting device. The light-emitting device in FIG. 3 comprises an anode (reflective electrode) 2, a hole injection layer 3, a hole transport layer 4, an emissive layer 5, a first electron transport layer 6, a second electron transport layer 7, an electron injection layer 8, and a cathode (light extraction electrode) 9, stacked in this order on an opaque, light-impermeable substrate 1. Furthermore, a first protective layer 10, a second protective layer 11, and a third protective layer 12 are provided as sealing films, and in some cases, a microlens (not shown) is also provided. When a voltage is applied between the two electrodes, holes are injected from the anode 2 side and electrons are injected from the cathode 9 side. The injected holes and electrons recombine in the emissive layer 5, forming an excited state, and then emit light when returning to the ground state. The emitted light is reflected by the reflective electrode 2 and output from the light extraction electrode 9 side.

[0017] 3, the anode (reflective electrode) 2 is the first electrode, the hole injection layer 3, the hole transport layer 4, the light-emitting layer 5, the first electron transport layer 6, the second electron transport layer 7, and the electron injection layer 8 are organic compound layers, and the cathode (light extraction electrode) 9 is the second electrode. The hole injection layer 3 and the hole transport layer 4 are first organic compound layers, and the first electron transport layer 6, the second electron transport layer 7, and the electron injection layer 8 are second organic compound layers.

[0018] In the present invention, the exposure spectrum emitted from the exposure head is a spectrum having multiple peaks, preferably a spectrum having multiple peaks with a wavelength spread and a certain degree of intensity. The inventors' investigations led to the following conclusions: That is, an emission spectrum having multiple peaks is superior in the series of mechanisms that efficiently excite the photosensitive layer of the photoreceptor and rapidly transfer charge to the charge transport material, and is therefore considered to be one of the factors that can reduce residual charge and prevent a deterioration in image quality. In particular, a spectrum having multiple peaks with a wavelength spread has a range of light energy, making it possible to irradiate various excitation energies as excitation light. Therefore, when the photosensitive material in the photosensitive layer is excited, charge separation occurs in various energy states, which facilitates charge migration and is thought to lead to a reduction in residual charge. Conversely, in the case of strong excitation light with a single wavelength, charge separation occurs in the same energy state, which is thought to generate excess charge that is difficult to transfer, increasing the probability of it becoming residual charge.

[0019] The inventors have discovered that organic light-emitting devices with a top-emission device structure using an opaque substrate and utilizing optical interference, as shown in Figure 3, are effective in achieving light with multiple peaks, particularly intense light with multiple peaks over a broad wavelength range. This structure enables the emission spectrum inherent to the light-emitting material to be extracted as a spectrum with multiple peaks over a broader bandwidth. Specifically, the film thickness between the light-emitting layer 5 and the reflective electrode 2, the film thickness between the light-emitting layer 5 and the light-extraction electrode 9, and the total organic film thickness are preferably set to interference film thicknesses that enhance the emission wavelength. To further enhance the effect, the film thickness of the first protective layer 10, the film thickness of the second protective layer 11, the film thickness of the third protective layer 12, and the light reflectance of the second protective layer 11 can be optimized. Optimizing the film thickness and reflectance of these protective layers enables the creation of a short-period optical interference structure, enabling the emission spectrum inherent to the light-emitting material to be extracted as a spectrum with multiple peaks.

[0020] The organic light-emitting element preferably has an optical resonator structure formed by the anode 2 and the cathode 9. The optical resonator structure is configured, for example, so that the optical distance between the electrodes is a distance that intensifies the light emitted from the light-emitting layer. As an example, the distance from the light-emitting layer to the reflective layer on the substrate side is an odd multiple of λ / 4, where λ is the wavelength of the light emitted from the light-emitting layer.

[0021] Assuming that manufacturing errors and the like are allowed, it is preferable that the optical distance L1 satisfy the following formula 1. The optical distance L1 may be the distance from the light-emitting layer to the reflective layer on the substrate side, the distance from the light-emitting layer to the reflective layer on the light extraction side, or the distance from the reflective layer on the substrate side to the reflective layer on the light extraction side. 0.7(-Φ1 / (2π)+m1)×λ≦2×L1≦1.2(-Φ1 / (2π)+m1)×λ...Formula 1 In Equation 1, λ is the wavelength of light emitted from the light-emitting layer, Φ1 is the phase shift at the reflecting surface, and m1 is an integer. When there are two reflecting surfaces, Φ1 is the sum of the phase shifts.

[0022] The cathode 9 may be a semi-transmissive reflective layer that transmits a portion of light reaching its surface and reflects the other portion (i.e., semi-transmissive reflectivity). The semi-transmissive reflective electrode is formed from a single metal such as magnesium or silver, an alloy primarily composed of magnesium or silver, or an alloy material containing an alkali metal or alkaline earth metal. For example, magnesium-silver, aluminum-lithium, aluminum-magnesium, silver-copper, zinc-silver, etc. can be used. These electrode materials may be used alone or in combination of two or more. The cathode 9 may have a single-layer structure or a multi-layer structure. Among these, silver is preferred, and a silver alloy is even more preferred to reduce silver aggregation. The alloy ratio is not important as long as silver aggregation can be reduced. For example, the silver:other metal ratio may be 1:1, 3:1, etc. The other metal is preferably magnesium.

[0023] To achieve the optimal spectral shape, the thickness of the first protective layer 10 is preferably 100 nm to 3000 nm, more preferably 500 nm to 2000 nm, the thickness of the second protective layer 11 is preferably 10 nm to 500 nm, more preferably 50 nm to 300 nm, and the thickness of the third protective layer 12 is preferably 100 nm to 2000 nm, more preferably 200 nm to 1000 nm. Furthermore, the protective layer is not limited to a three-layer structure, and may have a multilayer structure of four or more layers. The multilayer structure facilitates optimization of the interference period. The protective layer preferably contains silicon nitride, and preferably has a layer containing aluminum oxide on a layer containing silicon nitride.

[0024] Furthermore, in order to efficiently irradiate the photoconductor with the high-brightness emission spectrum emitted from the light-emitting layer 5, it is preferable to reduce the absorption loss that occurs on the optical path from the light-emitting layer 5 to the surface of the photoconductor. First, it is desirable that the light is not absorbed by carrier transport layers other than the light-emitting layer 5. In particular, it is preferable that the light is not absorbed by the hole transport layer 4 located between the reflective electrode (anode) 2 and the light-emitting layer 5, since the emission spectrum passes through the layer at least twice. Second, it is desirable that the light is not absorbed by the protective layer or microlenses on the light extraction electrode 9. Third, it is desirable that the light is not absorbed by the lens array provided between the organic light-emitting element and the photoconductor.

[0025] <Exposure head spectrum> Photoreceptors are composed of various functional layers. Among these, the charge generation layer plays a role in forming a charge separation state by exposure to light. Within the charge generation layer, the charge generation material is an important material that plays a role in photoelectron conversion. Examples of charge generation materials include azo pigments, perylene pigments, anthraquinone derivatives, anthanthrone derivatives, dibenzpyrenequinone derivatives, pyranthrone derivatives, quinone pigments, indigoid pigments, phthalocyanine pigments, and perinone pigments. Among these, phthalocyanine pigments are preferred. Among phthalocyanine pigments, oxytitanium phthalocyanine, chlorogallium phthalocyanine, and hydroxygallium phthalocyanine are preferred.

[0026] In recent years, organic light-emitting devices have been proposed as exposure light sources for photoreceptors. A typical organic light-emitting device is a bottom-emission organic light-emitting device, which is considered to have a relatively simple manufacturing process. In this case, the emission spectrum is extracted from the transparent substrate side where the driving pixel circuitry is located, potentially reducing light utilization efficiency. Furthermore, bottom-emission organic light-emitting devices are difficult to fabricate with an interference film structure that enhances light emission, which may result in low exposure efficiency as an exposure light source. One solution to this problem is organic light-emitting devices that emit strong light with a broad wavelength range, as mentioned above. Among organic light-emitting devices, top-emission organic light-emitting devices, which can utilize optical interference, are preferred. A broad wavelength range of light results in a certain range of light energy. In this case, specific excitation energy is not concentrated in the charge-generating material that absorbs light, which is thought to lead to the reduction of excess charge. It is thought that various conductive paths, rather than just a certain type, are generated, resulting in efficient charge separation.

[0027] Fig. 4 shows an example of the spectrum of the exposure head of the present invention, in which 40 is the PL spectrum of the luminescent material contained in the luminescent layer, 41 is the exposure spectrum emitted from the exposure head, 42 is the light absorption spectrum of the photoreceptor, 43 is the light absorption spectrum of the first organic compound layer, and 44 is the light absorption spectrum of the second organic compound layer.

[0028] As shown in Figure 4(a), the number of peaks in the exposure spectrum 41 is greater than the number of peaks in the PL spectrum 40 of the light-emitting material. In Figure 4(a), the PL spectrum 40 of the light-emitting material has two peaks, while the exposure spectrum 41 has five or more peaks.

[0029] 4(a), it is preferable that all peaks of the exposure spectrum 41 overlap with the photoreceptor's light absorption spectrum 42. If the overlap between the multiple peaks of the exposure spectrum 41 and the photoreceptor's light absorption spectrum 42 is poor, the charge separation efficiency may be poor and more intense light may be required, which may increase the electrical load on the organic light-emitting element.

[0030] As shown in Figures 4(a) and 4(b), it is preferable that the longest peak wavelength in the light absorption spectrum 44 of the second organic compound layer is farther from the maximum emission peak wavelength of the PL spectrum 40 of the light-emitting material than the longest peak wavelength in the light absorption spectrum 43 of the first organic compound layer.

[0031] 4(a) and 4(b), the maximum emission peak wavelength of the PL spectrum 40 of the light-emitting material is preferably closer to the maximum absorption peak wavelength in the visible light region of the light absorption spectrum 42 of the photoreceptor than to the longest peak wavelength in the light absorption spectrum 43 of the first organic compound layer or the longest peak wavelength in the light absorption spectrum 44 of the second organic compound layer. Furthermore, as shown in FIG. 4(b), the maximum emission peak wavelength of the exposure spectrum 41 is preferably closer to the maximum absorption peak wavelength in the visible light region of the light absorption spectrum 42 of the photoreceptor than to the longest peak wavelength in the light absorption spectrum 43 of the first organic compound layer or the longest peak wavelength in the light absorption spectrum 44 of the second organic compound layer.

[0032] Furthermore, it is desirable that there be little overlap between the exposure spectrum 41 and the absorption spectrum of the protective layer. If there is a large overlap with the absorption spectrum of the protective layer, the spectrum may be strongly affected by the interference of light generated within the protective layer, which may significantly reduce the spectral intensity. Similarly, it is desirable that there be little overlap between the exposure spectrum 41 and the absorption spectrum of each layer constituting the organic compound layer.

[0033] <Layer structure of organic light-emitting element> Specific examples of the organic light-emitting device of this embodiment include a multilayer structure in which electrode layers and organic compound layers shown in (1) to (6) below are sequentially stacked on a substrate. In any of the structure, the organic compound layers always include a light-emitting layer containing a light-emitting material. (1) Anode / Emitting layer / Cathode (2) Anode / hole transport layer / light-emitting layer / electron transport layer / cathode (3) Anode / hole transport layer / light-emitting layer / electron transport layer / electron injection layer / cathode (4) Anode / hole injection layer / hole transport layer / light-emitting layer / electron transport layer / cathode (5) Anode / hole injection layer / hole transport layer / light-emitting layer / electron transport layer / electron injection layer / cathode (6) Anode / hole transport layer / electron blocking layer / light-emitting layer / hole blocking layer / electron transport layer / cathode However, these examples of device configurations are merely very basic device configurations and are not limited to these. For example, various layer configurations can be adopted, such as providing an insulating layer, an adhesive layer, or an interference layer at the interface between the electrode and the organic compound layer, configuring the electron transport layer or hole transport layer from two layers with different ionization potentials, or configuring the light-emitting layer from two layers made of different light-emitting materials.

[0034] <Compounds used in organic light-emitting devices> In the organic light-emitting device according to this embodiment, conventionally known low-molecular-weight and high-molecular-weight hole-injecting or hole-transporting compounds, host compounds, light-emitting compounds, electron-injecting or electron-transporting compounds, etc. may be used together as needed. Examples of these compounds are listed below.

[0035] As the hole injection transport material, a material with high hole mobility is preferred, which facilitates the injection of holes from the anode and transports the injected holes to the light-emitting layer. Furthermore, a material with a high glass transition temperature is preferred to reduce deterioration of film quality, such as crystallization, in organic light-emitting devices. Examples of low-molecular-weight and high-molecular-weight materials with hole injection and transport properties include triarylamine derivatives, arylcarbazole derivatives, phenylenediamine derivatives, stilbene derivatives, phthalocyanine derivatives, porphyrin derivatives, poly(vinylcarbazole), poly(thiophene), and other conductive polymers. Furthermore, the above-mentioned hole injection and transport materials are also suitable for use in electron blocking layers. Specific examples of compounds usable as hole injection and transport materials are listed below, but the present invention is not limited to these.

[0036] [ka]

[0037] Examples of light-emitting materials that are primarily involved in light-emitting function include fused ring compounds (e.g., fluorene derivatives, naphthalene derivatives, pyrene derivatives, perylene derivatives, tetracene derivatives, anthracene derivatives, rubrene, etc.), quinacridone derivatives, coumarin derivatives, stilbene derivatives, organoaluminum complexes such as tris(8-quinolinolato)aluminum, iridium complexes, platinum complexes, rhenium complexes, copper complexes, europium complexes, ruthenium complexes, and polymer derivatives such as poly(phenylenevinylene) derivatives, poly(fluorene) derivatives, and poly(phenylene) derivatives. Specific examples of compounds that can be used as light-emitting materials are shown below, but are not limited to these.

[0038] [ka]

[0039] [ka]

[0040] Specific examples of the host or assist contained in the light-emitting layer include, but are not limited to, aromatic hydrocarbon compounds or derivatives thereof, carbazole derivatives, azine derivatives, xanthone derivatives, dibenzofuran derivatives, dibenzothiophene derivatives, organic aluminum complexes such as tris(8-quinolinolato)aluminum, and organic beryllium complexes. Specific examples are shown below.

[0041] [ka]

[0042] The electron transporting material can be arbitrarily selected from those capable of transporting electrons injected from the cathode to the light-emitting layer, and is selected taking into consideration the balance with the hole mobility of the hole transporting material. Examples of materials having electron transporting properties include oxadiazole derivatives, oxazole derivatives, pyrazine derivatives, triazole derivatives, triazine derivatives, quinoline derivatives, quinoxaline derivatives, phenanthroline derivatives, organoaluminum complexes, and fused ring compounds (e.g., fluorene derivatives, naphthalene derivatives, chrysene derivatives, anthracene derivatives, etc.). Furthermore, the above electron transporting materials are also suitable for use in hole-blocking layers. Specific examples of compounds used as electron transporting materials are shown below, but of course, are not limited to these.

[0043] [ka]

[0044] The electron injection material can be selected from those that allow easy electron injection from the cathode, taking into consideration the balance with hole injection properties, etc. Examples of organic compounds include n-type dopants and reducing dopants. Examples include compounds containing alkali metals such as lithium fluoride, lithium complexes such as lithium quinolinol, benzimidazolidene derivatives, imidazolidene derivatives, fulvalene derivatives, and acridine derivatives. They can also be used in combination with the above-mentioned electron transport materials.

[0045] <Configuration of organic light-emitting element> The organic light-emitting element is provided by forming a first electrode, an organic compound layer, and a second electrode on a substrate. An insulating layer may be provided on the substrate. A protective layer, a color filter, a microlens, etc. may be provided on the second electrode. When a color filter is provided, a planarizing layer may be provided between the protective layer. The planarizing layer may be made of acrylic resin, etc. The same applies when a planarizing layer is provided between the color filter and the microlens. Either the first electrode or the second electrode may be an anode, and the other may be a cathode.

[0046] [substrate] Examples of the substrate include quartz, glass, a silicon wafer, a resin, and a metal. Furthermore, the substrate may be provided with a switching element such as a transistor and wiring, and an insulating layer thereon. Any material can be used for the insulating layer, as long as it allows for the formation of a contact hole so that wiring can be formed between the first electrode and the insulating layer, and ensures insulation from wiring that is not connected. For example, resins such as polyimide, silicon oxide, silicon nitride, etc. can be used.

[0047] [electrode] A pair of electrodes can be used. The pair of electrodes may be an anode and a cathode. When an electric field is applied in the direction in which the organic light-emitting element emits light, the electrode with a higher potential is the anode, and the other is the cathode. It can also be said that the electrode that supplies holes to the light-emitting layer is the anode, and the electrode that supplies electrons is the cathode.

[0048] The anode material should have as high a work function as possible. Examples include simple metals such as gold, platinum, silver, copper, nickel, palladium, cobalt, selenium, vanadium, and tungsten, mixtures containing these metals, alloys of these metals, and metal oxides such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and zinc indium oxide. Conductive polymers such as polyaniline, polypyrrole, and polythiophene can also be used.

[0049] These electrode materials may be used alone or in combination of two or more. The anode may be composed of one layer or multiple layers.

[0050] When used as a reflective electrode, for example, chromium, aluminum, silver, titanium, tungsten, molybdenum, or alloys or laminates thereof can be used. The above materials can also function as a reflective film without functioning as an electrode. When used as a transparent electrode, transparent conductive oxide layers such as indium tin oxide (ITO) and indium zinc oxide can be used, but are not limited to these. Photolithography techniques can be used to form the electrode.

[0051] On the other hand, materials with a low work function are preferred for the cathode. Examples include alkali metals such as lithium, alkaline earth metals such as calcium, and metals such as aluminum, titanium, manganese, silver, lead, and chromium, as well as mixtures containing these metals. Alternatively, alloys combining these metals can be used. For example, magnesium-silver, aluminum-lithium, aluminum-magnesium, silver-copper, and zinc-silver can be used. Metal oxides such as indium tin oxide (ITO) can also be used. These electrode materials can be used alone or in combination. The cathode can have either a single-layer or multi-layer structure. Among these, silver is preferred, and a silver alloy is even more preferred to reduce silver aggregation. The alloy ratio is not critical as long as silver aggregation can be reduced. For example, the silver:other metal ratio can be 1:1, 3:1, or the like.

[0052] The cathode may be a top-emission element using an oxide conductive layer such as ITO, or a bottom-emission element using a reflective electrode such as aluminum (Al), and is not particularly limited. The method for forming the cathode is not particularly limited, but DC and AC sputtering methods are more preferred because they provide good film coverage and make it easier to reduce resistance.

[0053] [Organic compound layer] The organic compound layer may be formed as a single layer or as multiple layers. When multiple layers are included, they may be called hole injection layer, hole transport layer, electron blocking layer, light-emitting layer, hole blocking layer, electron transport layer, or electron injection layer depending on their functions. The organic compound layer is mainly composed of organic compounds but may also contain inorganic atoms or inorganic compounds. For example, the organic compound layer may contain copper, lithium, magnesium, aluminum, iridium, platinum, molybdenum, zinc, or the like. The organic compound layer may be disposed between the first electrode and the second electrode, or may be disposed in contact with the first electrode and the second electrode.

[0054] The organic compound layers (hole injection layer, hole transport layer, electron blocking layer, light emitting layer, hole blocking layer, electron transport layer, electron injection layer, etc.) constituting the organic light emitting device according to one embodiment of the present invention are formed by the method shown below.

[0055] The organic compound layer constituting the organic light-emitting device according to one embodiment of the present invention can be formed by dry processes such as vacuum deposition, ionization deposition, sputtering, plasma, etc. Alternatively, a wet process can be used in which the compound is dissolved in an appropriate solvent and a layer is formed by a known coating method (e.g., spin coating, casting, microgravure coating, gravure coating, bar coating, roll coating, wire bar coating, dip coating, spray coating, screen printing, flexographic printing, offset printing, inkjet printing, capillary coating, nozzle coating, LB method, etc.). Among these, vacuum deposition, ionization deposition, inkjet printing, nozzle coating, etc. are suitable for producing a large-area organic light-emitting device.

[0056] Here, when a layer is formed by a vacuum deposition method or a solution coating method, crystallization is unlikely to occur and the layer has excellent stability over time. When a film is formed by a coating method, the film can be formed by combining with an appropriate binder resin.

[0057] Examples of the binder resin include, but are not limited to, polyvinylcarbazole resin, polycarbonate resin, polyester resin, ABS resin, acrylic resin, polyimide resin, phenol resin, epoxy resin, silicone resin, and urea resin.

[0058] These binder resins may be used singly or in combination as homopolymers or copolymers, and may further contain known additives such as plasticizers, antioxidants, and ultraviolet absorbers, if necessary.

[0059] The thickness of each layer in the organic light-emitting device is preferably 1 nm to 10 μm in general, and particularly the thickness of the light-emitting layer of the organic compound layer is preferably 10 nm to 100 nm to obtain effective light-emitting characteristics.

[0060] [Charge Generation Layer] The charge generation layer may be formed by forming an n / p junction with a p layer and an n layer, or by using a p-doped layer or an n-doped layer. For example, when only a P / N junction is formed, it is preferable to provide an electron injection layer to further inject electrons extracted by the P layer into the electron transport layer. An n-doped layer / p-doped layer may also be used. The present invention is not limited to any particular combination of charge generation layers.

[0061] The p-doped layer may be made by mixing Lewis acids such as HAT-CN and molybdenum oxide, which have high electron-withdrawing properties, with aromatic amine compounds. HAT-CN and molybdenum oxide are n-type materials, which means that they can be stacked by withdrawing electrons. The p-doped layer or the np junction consisting of a stack of n-type material and p-type material is treated as a p-charge generation layer.

[0062] The n-doped layer is preferably made of a material with a low work function, such as an alkali metal or alkaline earth metal, which is easy to dope with electrons. In this invention, the n-doped layer is treated as an n-charge generation layer. Alternatively, an electron injection layer may be formed by combining a thin film of a reducing metal such as LiF, forming an n-type layer and a p-type layer to generate charges.

[0063] Examples of n dopants that can be used include alkali metals such as Li, Na, K, Rb, and Cs, alkaline earth metals such as Mg, Ca, Sr, and Ba, and rare earth metals such as Yb, as well as compounds thereof (alkali metal compounds (including oxides such as lithium oxide, halides, and carbonates such as lithium carbonate and cesium carbonate), alkaline earth metal compounds (including oxides, halides, and carbonates), and rare earth metal compounds (including oxides, halides, and carbonates).

[0064] [Protective layer] A protective layer may be provided on the second electrode. For example, by adhering glass with a moisture absorbent on the second electrode, the infiltration of water and other contaminants into the organic compound layer can be reduced, thereby reducing the occurrence of display defects. In another embodiment, a passivation film such as silicon nitride may be provided on the second electrode to reduce the infiltration of water and other contaminants into the organic compound layer. For example, after forming the second electrode, the second electrode may be transferred to another chamber without breaking the vacuum, and a 2 μm-thick silicon nitride film may be formed by CVD to serve as a protective layer. A protective layer may be provided using atomic layer deposition (ALD) after the CVD film formation. The material of the film formed by ALD is not limited, and may be silicon nitride, silicon oxide, aluminum oxide, or the like. Silicon nitride may be further formed on the film formed by ALD by CVD. The film formed by ALD may have a thickness smaller than that of the film formed by CVD. Specifically, the thickness may be 50% or less, or even 10% or less.

[0065] [Color Filter] A color filter may be provided on the protective layer. For example, a color filter taking into consideration the size of the organic light-emitting element may be provided on a separate substrate and then bonded to the substrate on which the organic light-emitting element is provided, or a color filter may be patterned on the protective layer described above using photolithography technology. The color filter may be made of a polymer.

[0066] [Planarization layer] A planarization layer may be provided between the color filter and the protective layer. The planarization layer is provided for the purpose of reducing the unevenness of the underlying layer. It may also be called a material resin layer without limiting its purpose. The planarization layer may be composed of an organic compound, and may be either a low molecular weight or a high molecular weight, but a high molecular weight is preferred.

[0067] The planarizing layer may be provided above or below the color filter, and may be made of the same or different materials, such as polyvinyl carbazole resin, polycarbonate resin, polyester resin, ABS resin, acrylic resin, polyimide resin, phenol resin, epoxy resin, silicone resin, and urea resin.

[0068] [Microlens] The organic light-emitting element may have an optical component such as a microlens on its light-emitting side. The microlens may be made of acrylic resin, epoxy resin, or the like. The microlens may be intended to increase the amount of light extracted from the organic light-emitting element and control the direction of the extracted light. The microlens may have a hemispherical shape. When the microlens has a hemispherical shape, among the tangents to the hemisphere, there is a tangent that is parallel to the insulating layer, and the point of contact between this tangent and the hemisphere is the vertex of the microlens. The vertex of the microlens can be determined in the same way in any cross-sectional view. In other words, among the tangents to the semicircle of the microlens in the cross-sectional view, there is a tangent that is parallel to the insulating layer, and the point of contact between this tangent and the semicircle is the vertex of the microlens.

[0069] It is also possible to define the midpoint of a microlens. In the cross section of the microlens, a line segment is imagined from the point where an arc shape ends to the point where another arc shape ends, and the midpoint of this line segment can be called the midpoint of the microlens. The cross section for determining the vertex and midpoint may be a cross section perpendicular to the insulating layer.

[0070] [Counter substrate] An opposing substrate may be provided on the planarization layer. The opposing substrate is called an opposing substrate because it is provided at a position corresponding to the aforementioned substrate. The constituent material of the opposing substrate may be the same as that of the aforementioned substrate. When the aforementioned substrate is defined as a first substrate, the opposing substrate may be a second substrate.

[0071] <Specific examples of exposure heads> 5 is a schematic diagram showing one form of a light-emitting device that can be used in the exposure head of this embodiment. The light-emitting device of this embodiment can be used as a light source for an image forming apparatus. The light-emitting device of this embodiment has a rectangular shape with long sides parallel to a first direction and short sides parallel to a direction intersecting the first direction, and the first direction may be, for example, a direction along the rotation axis of a photosensitive member of the image forming apparatus.

[0072] The substrate 1701 has a polygonal shape, and an example of a rectangular substrate 1701 will be described here. In this specification, the direction of the long sides of the rectangular substrate 1701 is referred to as the first direction, and the direction of the short sides perpendicular to the long side is referred to as the second direction. In addition, the polygon in this specification also includes shapes with rounded corners. A moisture-resistant ring 1700 is disposed on the rectangular substrate 1701, and serves to reduce and prevent moisture from penetrating into the light-emitting device. The moisture-resistant ring 1700 can be, for example, a guard ring formed of a wiring layer.

[0073] A light-emitting region 1702, a contact region 1703, pads 1704, and a circuit 1706 are arranged inside the moisture-resistant ring 1700. In this embodiment, the contact region 1703 includes a first contact region 1703_1, a second contact region 1703_2, a third contact region 1703_3, a fourth contact region 1703_4, and a fifth contact region 1703_5. The pads 1704 include a first pad 1704_1, a second pad 1704_2, and a third pad 1704_3.

[0074] The circuit 1706 is a part of a circuit for driving each light-emitting device, and includes a circuit 1706_1 and a circuit 1706_2. Specific examples of the circuits 1706_1 and 1706_2 include, but are not limited to, an input protection circuit, an input circuit to which driving data is input, and a logic circuit for processing data.

[0075] Light-emitting elements EL are arranged in rows and columns in the light-emitting region 1702. Wiring that electrically connects to a common electrode of the light-emitting elements EL is arranged in the contact region 1703. Pads 1704_1 electrically connect the contact region 1703 to an external element.

[0076] The outer circumferential shape of the moisture-resistant ring 1700 may include a plurality of recessed portions (recesses 1705), which can be used as contact regions for contacting ribs that are part of a vapor deposition mask in a film-forming process, for example.

[0077] As described above, each of the plurality of light-emitting elements EL arranged in a matrix in the light-emitting region 1702 is composed of a light-emitting layer and a first electrode and a second electrode that sandwich the light-emitting layer. In this embodiment, an example is shown in which the first electrode is an independent electrode provided for each light-emitting element EL, and the second electrode is a common electrode provided in common to all the light-emitting elements EL.

[0078] For example, in the case where light-emitting region 1702 has four rows of light-emitting elements EL, the initial positions of the light-emitting elements EL in the first row and the first positions of the light-emitting elements EL in the second row may be shifted in the X direction by ¼ of the dimension of the light-emitting elements EL in the X direction (first direction), as illustrated in Fig. 5. In the case of n rows, where n is an integer of 2 or greater, the initial positions of the light-emitting elements EL in the first row and the first positions of the light-emitting elements EL in the second row may be shifted in the X direction by 1 / n of the dimension of the light-emitting elements EL in the X direction. Such a configuration is advantageous for improving resolution.

[0079] The contact region 1703 is an area adjacent to the light emitting region 1702 of the substrate 1701, and is disposed inside the moisture-resistant ring 1700. At least one of the contact region 1703, the pad 1704, and the circuit 1706, together with the recess 1705 of the moisture-resistant ring 1700, may be disposed between the light emitting region 1702 and one long side end of the substrate 1701, and may be disposed in series in the long side direction.

[0080] In this way, by providing the contact region 1703, the pad 1704, the circuit 1706, etc. at the same position in the short side direction, the length of the light emitting device in the short side direction can be reduced, making it possible to miniaturize the light emitting device.

[0081] The light-emitting device of this embodiment has multiple contact regions 1703 between the common electrode of the light-emitting element EL and the power supply wiring along the long side edge of the light-emitting device. If the common electrode is made of, for example, a transparent electrode material with relatively high electrical resistance, the amount of voltage drop in the long side direction may be large. Therefore, the voltage applied to each light-emitting element EL varies depending on the distance from the contact region 1703 to which the potential is supplied. This may result in differences in actual emission brightness between light-emitting elements EL to which a voltage is applied to emit light with the same brightness, resulting in shading and other issues. By having multiple contact regions 1703 along the long side edge of the light-emitting device, as in this embodiment, the voltage drop of the common electrode in the long side direction can be reduced, thereby reducing the occurrence of shading and other issues.

[0082] In this embodiment, an example in which a light-emitting device is used in a head substrate 1800 of an exposure head of an image forming apparatus will be described with reference to Fig. 6. Fig. 6(a) is a schematic perspective view of the head substrate 1800. Fig. 6(b) shows an arrangement of a plurality of light-emitting elements EL provided on the head substrate 1800, and Fig. 6(c) shows an enlarged view of a portion of Fig. 6(b).

[0083] An LED chip 1803 is mounted on the head substrate 1800. As the LED chip 1803, for example, the light emitting device shown in FIG.

[0084] 6(a), an LED chip 1803 is provided on one surface of the head substrate 1800, and a long flexible flat cable (FFC) connector 1807 is provided on the other surface. The one surface of the head substrate 1800 here refers to the surface (upper surface, front surface) on which the LED chip 1803 is provided. The other surface of the head substrate 1800 refers to the surface (lower surface, back surface) opposite to the side on which the LED chip 1803 is provided.

[0085] The FFC connector 1807 is attached to the other surface (bottom surface, back surface) of the head substrate 1800 so that its longitudinal direction follows the longitudinal direction of the head substrate 1800. The long FFC connector 1807 is provided to input a control signal (drive signal) from a control circuit section of the main body of the image forming apparatus, and the control signal is transferred to each LED chip 1803. The LED chips 1803 are driven (to emit light or turn off) by the control signal input to the head substrate 1800.

[0086] The LED chips 1803 mounted on the head substrate 1800 will now be described. As shown in Fig. 6(b) and Fig. 6(c), a plurality of LED chips 1803 are arranged on one surface of the head substrate 1800. For example, LED chips 1803_1 to 1803_29 (29 chips) are arranged. Fig. 6(b) illustrates LED chips 1803_1, 1803_13, 1803_14, 1803_15, 1803_16, and 1803_29. Each of the LED chips 1803_1 to 1803_29 has a plurality of light-emitting elements EL arranged in its longitudinal direction, and for example, 516 light-emitting elements EL are arranged.

[0087] In the longitudinal direction of the LED chip 1803, the center-to-center distance k2 between adjacent light-emitting elements EL corresponds to the resolution of the image forming device. For example, when the resolution of the image forming device in this embodiment is 1200 dpi, the light-emitting elements EL are arranged so that the center-to-center distance k2 between adjacent light-emitting elements EL is 21.16 μm in the longitudinal direction of the LED chips 1803_1 to 1803_29. Therefore, the exposure range of the exposure head in this embodiment is approximately 314 mm.

[0088] The photosensitive layer of the photosensitive drum is formed with a width of 314 mm or more. Since the long side of A4 size recording paper and the short side of A3 size recording paper are 297 mm, the exposure head of this embodiment has an exposure range that can form images on A4 size recording paper and A3 size recording paper. Note that while Figure 6(b) shows an example in which multiple light-emitting elements EL are arranged in the longitudinal direction, light-emitting elements EL may be arranged in the lateral direction as well as the longitudinal direction.

[0089] A plurality of LED chips 1803_1 to 1803_29 are arranged in the axial direction of the photosensitive drum. Specifically, the LED chips 1803_1 to 1803_29 are alternately arranged in two rows along the axial direction of the photosensitive drum. That is, as shown in FIG. 6(b), counting from the left, odd-numbered LED chips 1803_1, 1803_3, ..., 1803_29 are mounted in a row in the longitudinal direction of the head substrate 1800. Also, counting from the left, even-numbered LED chips 1803_2, 1803_4, ..., 1803_28 are mounted in a row in the longitudinal direction of the head substrate 1800. The LED chips 1803 are arranged in this manner.

[0090] 6(c), the center-to-center distance k1 of the light-emitting elements EL can be made equal to the center-to-center distance k2 of the light-emitting elements EL in the longitudinal direction of the LED chip 1803. Here, the center-to-center distance k1 of the light-emitting elements EL refers to the center-to-center distance between the light-emitting elements EL arranged at one end of the LED chip 1803_13 and the other end of the LED chip 1803_14. The center-to-center distance k2 of the light-emitting elements EL refers to the center-to-center distance k2 between adjacent light-emitting elements EL in the LED chip 1803_14. In other words, the center-to-center distance k1 of the adjacent light-emitting elements EL arranged at one end of the LED chip 1803 and the other end of the other LED chip 1803 can be made equal to the center-to-center distance k2 of the adjacent light-emitting elements EL on one LED chip 1803.

[0091] In this embodiment, the light-emitting element EL is an organic light-emitting element that is a current-driven light-emitting element. The organic light-emitting elements are arranged in a line along the main scanning direction (the axial direction of the photosensitive drum) on a TFT (Thin Film Transistor) substrate, for example, and are electrically connected in parallel by power supply wiring that is also provided along the main scanning direction.

[0092] When the light-emitting device is used in an exposure head, linear exposure is performed, so the ratio of the longitudinal direction (first direction X) to the lateral direction (second direction Y) of the shape of the light-emitting region 1702 is larger than when the light-emitting device is used in a display device or the like. The ratio of the longitudinal direction (first direction X) to the lateral direction (second direction Y) of the shape of the LED chip substrate is also larger. Specifically, for example, the length of the long side of the LED chip 1803 (or the light-emitting region 1702) is 5 times or more the length of the short side of the LED chip 1803 (or the light-emitting region 1702), and may be 10 times or more the length of the short side of the LED chip 1803 (or the light-emitting region 1702). For example, the length of the long side of the LED chip 1803 (or the light-emitting region 1702) can be 20 times or more the length of the short side of the LED chip 1803 (or the light-emitting region 1702).

[0093] The length of the long side of the LED chip 1803 is determined by the axial length of the photosensitive drum, the number of LED chips arranged in the axial direction, and the arrangement of the LED chips 1803. The length of the short side of the LED chip 1803 is determined by whether the light-emitting element EL is arranged in the light-emitting region 1702 in the direction perpendicular to the axis of the photosensitive drum, and the arrangement of the pad 1704 and the contact region 1703.

[0094] Furthermore, the organic compound layer of the light-emitting element EL can be configured to have a light-emitting layer that emits red light in consideration of the wavelength dependency of the photosensitivity of the photosensitive drum.

[0095] The LED chip 1803 may have a color filter, which can improve print quality by absorbing stray light from unintended directions without reducing the amount of normal light incident on the photosensitive drum.

[0096] ≪Photoreceptor≫ An example of the layer structure of the photoreceptor of the present disclosure is shown in Figure 7. In Figure 7, an undercoat layer 122, a charge generation layer 123, a charge transport layer 124, and a protective layer 125 are laminated on a support 121. As shown in Figure 7, the photosensitive layer may be a laminated photosensitive layer having the charge generation layer 123 and the charge transport layer 124, or may be a single-layer photosensitive layer containing a charge generation material and a charge transport material.

[0097] A method for producing the photoreceptor of the present disclosure includes preparing a coating liquid for each layer described below, coating the desired layers in order, and drying the coating liquid. Examples of methods for applying the coating liquid include dip coating, spray coating, inkjet coating, roll coating, die coating, blade coating, curtain coating, wire bar coating, and ring coating. Among these, dip coating is preferred from the viewpoints of efficiency and productivity.

[0098] The configuration of the photoreceptor of the present disclosure will be described below. <Support 121> The support 121 of the photoreceptor is preferably conductive (conductive support). The support in the present disclosure has a drum (cylindrical) shape. The surface of the support may be subjected to electrochemical treatment such as anodizing, blasting, cutting, or the like.

[0099] The material of the support 121 is preferably metal, resin, glass, or the like. Examples of metals include aluminum, iron, nickel, copper, gold, stainless steel, and alloys thereof. Of these, an aluminum support is preferable. It is also preferable to impart conductivity to resin or glass by processing such as mixing or coating with a conductive material.

[0100] <Undercoat layer 122> In the present disclosure, an undercoat layer 122 may be provided on the support 121. The undercoat layer 122 is provided for the purposes of improving the adhesion of the photosensitive layer, improving coating properties, improving charge injection from the support 121, protecting the photosensitive layer from electrical breakdown, and reducing interference fringes due to scattering of image exposure. The undercoat layer 122 may be a single undercoat layer containing one of the materials listed below, or may be a laminate of two or more different undercoat layers containing one of the materials listed below.

[0101] Examples of metal oxide particles include particles of indium tin oxide, tin oxide, indium oxide, titanium oxide, strontium titanate, zinc oxide, and aluminum oxide. Silicon dioxide particles can also be used. Examples of metal particles include particles of gold, silver, and aluminum. From the viewpoints of dispersibility in the coating solution for the undercoat layer and the electrical properties of the photoreceptor, the primary particle size of the metal oxide particles is preferably a number-average particle size of 0.1 μm or less. In the present disclosure, two or more types of metal oxide particles may be used in combination, such as those with different types of metal oxide, different types of surface treatment, or different particle sizes or specific surface areas.

[0102] The metal oxide particles contained in the undercoat layer 122 may be particles whose surfaces have been treated with a surface treatment agent such as a silane coupling agent in order to reduce black dot-like image defects caused by charge injection from the support 121 to the photosensitive layer side. A common method can be used to surface treat the metal oxide particles. Examples include dry and wet methods.

[0103] In the dry method, metal oxide particles are stirred in a mixer capable of high-speed stirring, such as a Henschel mixer, and an alcohol aqueous solution, organic solvent solution, or aqueous solution containing a surface treatment agent is added to the metal oxide particles to uniformly disperse them, followed by drying.

[0104] In the wet method, metal oxide particles and a surface treatment agent are stirred in a solvent or dispersed in a sand mill using glass beads or the like, and the solvent is then removed by filtration or vacuum distillation. After the solvent is removed, the mixture is preferably baked at 100°C or higher.

[0105] The undercoat layer 122 preferably contains a resin. Alternatively, the undercoat layer may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group.

[0106] Examples of resins include acrylic resins, allyl resins, alkyd resins, ethyl cellulose resins, ethylene-acrylic acid copolymers, epoxy resins, casein resins, and silicone resins. Examples include gelatin resins, phenolic resins, urethane resins, butyral resins, polyacrylate resins, polyacetal resins, polyamide-imide resins, polyamide resins, polyallyl ethers, polyimide resins, polyester resins, and polyethylene resins. Other examples include polycarbonate resins, polystyrene resins, polysulfone resins, polyvinyl alcohol resins, polybutadiene resins, and polypropylene resins. Among these, urethane resins with low hygroscopicity are preferred from the viewpoint of reducing potential fluctuations in high-temperature, high-humidity environments.

[0107] Examples of the polymerizable functional group include an isocyanate group, a blocked isocyanate group, a methylol group, an alkylated methylol group, an epoxy group, a metal alkoxide group, a hydroxy group, an amino group, a carboxy group, a thiol group, a carboxylic anhydride group, and a carbon-carbon double bond group.

[0108] The mass ratio (P / B) of the metal oxide particles (P) to the binder resin (B) in the undercoat layer 122 is preferably 1.0 / 1.0 or more and 3.0 / 1.0 or less.

[0109] Furthermore, for the purpose of improving electrical properties, the undercoat layer 122 may further contain an electron transport material, metal particles, a conductive polymer, etc. Among these, it is preferable to use an electron transport material.

[0110] Examples of electron transport substances include quinone compounds, imide compounds, benzimidazole compounds, cyclopentadienylidene compounds, fluorenone compounds, oxadiazole compounds, diphenoquinone compounds, xanthone compounds, alizarin compounds, benzophenone compounds, cyanovinyl compounds, aryl halide compounds, silole compounds, and boron-containing compounds.

[0111] The undercoat layer may be formed as a cured film by using an electron transporting substance having a polymerizable functional group as the electron transporting substance and copolymerizing it with the above-mentioned monomer having a polymerizable functional group.

[0112] For example, to adjust surface roughness, promote light scattering, or reduce cracking, the undercoat layer 122 may further contain organic resin particles or a leveling agent. As the organic resin particles, hydrophobic organic resin particles such as silicone particles or hydrophilic organic resin particles such as cross-linked polymethacrylate resin (PMMA) particles can be used.

[0113] The undercoat layer 122 may further contain additives, such as conductive material particles such as carbon black, charge transport materials, metal chelate compounds, organometallic compounds, and other known materials.

[0114] The undercoat layer 122 can be formed by preparing a coating solution for the undercoat layer containing the above-mentioned materials and solvent, forming a coating film of this on the support 121 or the conductive layer, and drying and / or curing it. Examples of solvents used in the coating solution for the undercoat layer include organic solvents such as alcohols, sulfoxides, ketones, ethers, esters, halogenated aliphatic hydrocarbons, and aromatic compounds. In the present disclosure, it is preferable to use alcohol-based or ketone-based solvents. Examples of dispersion methods for preparing the coating solution for the undercoat layer include methods using a homogenizer, ultrasonic disperser, ball mill, sand mill, roll mill, vibration mill, attritor, or high-speed liquid collision disperser.

[0115] The thickness of the undercoat layer 122 is preferably 0.1 μm or more, more preferably 0.2 μm or more, and particularly preferably 0.3 μm or more. The thickness of the undercoat layer 122 is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less.

[0116] <Photosensitive layer> The photosensitive layer of a photoreceptor is mainly classified into (1) a multi-layer photosensitive layer and (2) a single-layer photosensitive layer. (1) The multi-layer photosensitive layer is a photosensitive layer having a charge generation layer 123 containing a charge generation material and a charge transport layer 124 containing a charge transport material. (2) The single-layer photosensitive layer is a photosensitive layer containing both a charge generation material and a charge transport material.

[0117] (1) Laminated photosensitive layer The laminated photosensitive layer includes a charge generating layer 123 and a charge transport layer 124 .

[0118] (1-1) Charge generation layer 123 The charge generating layer 123 preferably contains a charge generating material and a resin.

[0119] Examples of charge-generating materials include azo pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, and phthalocyanine pigments. Among these, azo pigments and phthalocyanine pigments are preferred. Among phthalocyanine pigments, oxytitanium phthalocyanine pigments, chlorogallium phthalocyanine pigments, and hydroxygallium phthalocyanine pigments are preferred.

[0120] The content of the charge generating material in the charge generating layer 123 is preferably 40% by mass or more and 85% by mass or less, and more preferably 60% by mass or more and 80% by mass or less, based on the total mass of the charge generating layer 123.

[0121] Examples of the resin include polyester resin, polycarbonate resin, polyvinyl acetal resin, polyvinyl butyral resin, acrylic resin, silicone resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, polyvinyl alcohol resin, cellulose resin, polystyrene resin, polyvinyl acetate resin, polyvinyl chloride resin, etc. Among these, polyvinyl butyral resin is more preferred.

[0122] The charge generating layer 123 may further contain additives such as antioxidants and ultraviolet absorbers, etc. Specific examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, and benzophenone compounds.

[0123] The charge generating layer 123 can be formed by preparing a coating liquid for the charge generating layer containing the above-mentioned materials and solvent, forming a coating film of this on the undercoat layer 122, and drying it. Examples of solvents used in the coating liquid include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

[0124] The thickness of the charge generating layer 123 is preferably 0.1 μm or more and 1 μm or less, and more preferably 0.15 μm or more and 0.4 μm or less.

[0125] (1-2) Charge transport layer 124 The charge transport layer 124 preferably contains a charge transport material and a binder material. If the protective layer 125 described below is not provided, the charge transport layer 124 becomes the surface layer of the photoreceptor.

[0126] Examples of the charge transport material include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, triarylamine compounds, and resins having groups derived from these materials. Among these, triarylamine compounds are preferred.

[0127] The content of the charge transport material in the charge transport layer 124 is preferably 25% by mass to 70% by mass, and more preferably 30% by mass to 55% by mass, based on the total mass of the charge transport layer.

[0128] As the binder material, a thermoplastic resin (hereinafter also referred to as "resin") is used. Examples of the thermoplastic resin include polyester resin, polycarbonate resin, acrylic resin, and polystyrene resin. Among these, polycarbonate resin and polyester resin are preferred. As the polyester resin, polyarylate resin is particularly preferred.

[0129] The content ratio (mass ratio) of the charge transport material to the resin is preferably 4:10 to 20:10, and more preferably 5:10 to 12:10.

[0130] The charge transport layer 124 may also contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, etc. Specific examples of such additives include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, polystyrene resin particles, polyethylene resin particles, and boron nitride particles.

[0131] The charge transport layer 124 can be formed by preparing a coating solution for the charge transport layer containing the above-mentioned materials and solvent, forming a coating film of this on the charge generation layer 123, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Among these solvents, ether-based solvents and aromatic hydrocarbon-based solvents are preferred.

[0132] The thickness of the charge transport layer 124 is preferably 5 μm or more and 50 μm or less, more preferably 8 μm or more and 40 μm or less, and particularly preferably 10 μm or more and 30 μm or less.

[0133] (2) Single-layer photosensitive layer The single-layer photosensitive layer can be formed by preparing a coating solution for the photosensitive layer containing a charge generating material, a charge transporting material, a resin, and a solvent, forming the coating film on the undercoat layer 122, and drying it. The charge generating material, charge transporting material, and resin are the same as the examples of materials in "(1) Multilayer Photosensitive Layer" above.

[0134] <Protective layer 125> In the present disclosure, a protective layer 125 may be provided on the photosensitive layer. Durability can be improved by providing the protective layer 125. When the protective layer 125 is provided, the protective layer 125 becomes the surface layer of the photoreceptor.

[0135] The protective layer 125 may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group, which is the raw material for the binder. Examples of such reactions include thermal polymerization, photopolymerization, and radiation polymerization. Examples of the polymerizable functional group possessed by the monomer having the polymerizable functional group include an isocyanate group, a blocked isocyanate group, a methylol group, an alkylmethylol group, an epoxy group, a metal alkoxyl group, a hydroxyl group, an amino group, a carboxyl group, a thiol group, a carboxylic acid anhydride group, and a group containing a carbon-carbon double bond. Examples of the group containing a carbon-carbon double bond include an acryloyl group and a methacryloyl group. A monomer having charge transport capability may also be used as the monomer having the polymerizable functional group. Here, the cured product of the monomer having the polymerizable functional group serves as the binder material for the protective layer 125.

[0136] The monomer having a polymerizable functional group is preferably a hole transporting compound having a chain polymerizable functional group. The hole transporting compound having a chain polymerizable functional group is more preferably a compound represented by the following formula (CT-1) or (CT-2):

[0137] [ka]

[0138] In formula (CT-1), Ar 11 ~Ar 13are each independently a substituted aryl group or an unsubstituted aryl group. The substituent that the substituted aryl group may have is an alkyl group having 1 to 6 carbon atoms, or a monovalent functional group represented by any one of the following formulae (P-1) to (P-3). However, the compound represented by formula (CT-1) has at least one monovalent functional group represented by any one of the following formulae (P-1) to (P-3).

[0139] [ka]

[0140] In formula (CT-2), Ar 21 ~Ar 24 each independently represents a substituted aryl group or an unsubstituted aryl group, Ar 25 represents a substituted arylene group or an unsubstituted arylene group. The substituent that the substituted aryl group may have is an alkyl group having 1 to 6 carbon atoms, or a monovalent functional group represented by any of the following formulae (P-1) to (P-3). The substituent that the substituted arylene group may have is an alkyl group having 1 to 6 carbon atoms, or a monovalent functional group represented by any of the following formulae (P-1) to (P-3). However, the compound represented by formula (CT-2) has at least one monovalent functional group represented by any of the following formulae (P-1) to (P-3).

[0141] [ka] In formula (P-1), Z 11 represents a single bond or an alkylene group having 1 to 6 carbon atoms, and X 11 represents a hydrogen atom or a methyl group.

[0142] [ka] In formula (P-2), Z 21 represents a single bond or an alkylene group having 1 to 6 carbon atoms.

[0143] [ka] In formula (P-3), Z 31 represents a single bond or an alkylene group having 1 to 6 carbon atoms.

[0144] The protective layer 125 may contain fluorine atom-containing resin particles, which can improve the abrasion resistance of the protective layer.

[0145] Examples of resins contained in fluorine atom-containing resin particles include polytetrafluoroethylene resin, polychlorotrifluoroethylene resin, polytetrafluoroethylenepropylene resin, polyvinyl fluoride resin, polyvinylidene fluoride resin, and polydichlorodifluoroethylene resin. It is also preferable to use particles containing multiple types of these resins. Among these, from the viewpoint of improving dispersibility, it is more preferable that the fluorine atom-containing resin particles are polytetrafluoroethylene (PTFE) resin.

[0146] In cross-sectional observation of the protective layer 125, the fluorine atom-containing resin particles preferably have an arithmetic mean of the major axis of the primary particles (average primary particle size) measured from a secondary electron image taken with a scanning electron microscope of 150 nm or more and 300 nm or less, from the viewpoints of improving dispersibility and reducing potential fluctuations.More preferably, the fluorine atom-containing resin particles have an average primary particle size of 180 nm or more and 250 nm or less.

[0147] The content of the fluorine atom-containing resin particles in the protective layer 125 is preferably 5% by mass to 40% by mass, and more preferably 25% by mass to 35% by mass, based on the total mass of the protective layer.

[0148] The protective layer 125 may also contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, etc. Specific examples of the additives include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, polystyrene resin particles, polyethylene resin particles, and boron nitride particles.

[0149] The protective layer 125 can be formed by preparing a coating solution for the protective layer containing the above-mentioned materials and solvent, forming a coating film of this on the photosensitive layer, and drying and / or curing it. Examples of solvents used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, sulfoxide-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

[0150] The thickness of the protective layer 125 is preferably 0.50 μm or more and 10 μm or less, and more preferably 1 μm or more and 7 μm or less.

[0151] <Photoreceptor surface treatment> In the present disclosure, the surface of the photoreceptor may be treated. By performing the surface treatment, the behavior of the cleaning means (cleaning blade) that comes into contact with the photoreceptor can be further stabilized. Examples of surface treatment methods include a method in which a mold having convex portions is pressed against the surface of the photoreceptor to transfer the shape, a method in which an uneven shape is imparted by mechanical polishing, or a method in which powder is collided with the surface of the photoreceptor to roughen the surface. In this way, by providing concave or convex portions on the surface layer of the photoreceptor, the behavior of the cleaning means that comes into contact with the photoreceptor can be further stabilized.

[0152] The recesses or protrusions may be formed over the entire surface of the photoreceptor, or may be formed only on a portion of the surface of the photoreceptor. When the recesses or protrusions are formed only on a portion of the surface of the photoreceptor, it is preferable that the recesses or protrusions are formed over at least the entire area of ​​the contact region with the cleaning means (cleaning blade). When forming the recesses, a mold having protrusions corresponding to the recesses can be pressed against the surface of the photoreceptor to transfer the shape, thereby forming the recesses on the surface of the photoreceptor. [Example]

[0153] Example 1 <Organic light-emitting element> In this example, an organic EL device shown in Fig. 3 was fabricated. Specifically, a top-emission layered organic EL device was fabricated in which an anode (reflective electrode) 2, a hole injection layer 3, a hole transport layer 4, an emitting layer 5, a first electron transport layer 6, a second electron transport layer 7, an electron injection layer 8, a cathode (light extraction electrode) 9, a first protective layer 10, a second protective layer 11, and a third protective layer 12 were sequentially formed on a substrate 1. The emitting layer 5 was formed from a red emitting material and a host material.

[0154] A 40 nm titanium (Ti) film was deposited by sputtering on the silicon substrate 1, which had a wiring layer laminated on it, as the anode 2. This was then patterned using photolithography to form a square Ti pixel array and wiring. The pixel apertures were 20 μm on a side.

[0155] Next, the UV / ozone-cleaned silicon substrate and the material were placed in a vacuum deposition apparatus, and 1.0 × 10 -4 Pa(1×10 -6The chamber was evacuated to a pressure of 1000 psi (1 Torr). The hole injection layer 3 and hole transport layer 4 were then formed to thicknesses that would create an interference structure that intensified the emission wavelength. Next, an emitting layer 5 containing a red light-emitting material was formed. Next, a first electron transport layer 6, a second electron transport layer 7, and an electron injection layer 8 were formed in this order to thicknesses that would create an interference structure that intensified the emission wavelength. A cathode 9 was then formed. A silicon nitride film was formed by CVD as a first protective layer 10, an aluminum oxide film was formed by ALD as a second protective layer 11, and a silicon nitride film was formed by CVD as a third protective layer 12, in this order, to produce an organic light-emitting device. The emission spectrum of this organic light-emitting device was confirmed to be intense light with multiple peaks spanning a wavelength range from 500 nm to 800 nm.

[0156] <Exposure head and image forming device> Organic light-emitting diode (OLED) chips fabricated on a silicon substrate were cut and 17 chips were mounted on a PCB substrate. The PCB substrate with these OLED chips mounted was then installed in a housing with a lens array to fabricate an exposure head. Image evaluation was performed using a copier incorporating this exposure head, and it was confirmed that evaluation images could be stably output and that image defects were reduced by visual inspection, demonstrating the effectiveness of the present invention.

[0157] 4(a), it was confirmed that the number of peaks in the exposure spectrum 41 of the photosensitive drum exposed to light was greater than that in the PL spectrum 40 of the light-emitting material in the light-emitting layer. Furthermore, it was confirmed that all peaks in the exposure spectrum 41 overlapped with the absorption spectrum 42 of the photosensitive drum.

[0158] Example 2 The exposure spectrum of the exposure head prepared by the method described in Example 1, the absorption spectrum of the first organic compound layer (hole injection layer 3, hole transport layer 4) between the first electrode (anode 2) and the light-emitting layer 5, the absorption spectrum of the second organic compound layer (first electron transport layer 6, second electron transport layer 7, electron injection layer 8) between the second electrode (cathode 9) and the light-emitting layer 5, and the absorption spectrum of the charge-generating material used in the photoreceptor were all measured. As shown in Figures 4(a) and 4(b), it was confirmed that the maximum emission peak wavelengths of the PL spectrum 40 and exposure spectrum 41 of the light-emitting material are closer to the maximum absorption peak wavelength in the visible light region of the photoreceptor's light absorption spectrum 42 than the longest peak wavelengths of either the absorption spectrum 43 of the first organic compound layer or the absorption spectrum 44 of the second organic compound layer.

[0159] ≪Included components≫ The disclosure of this embodiment includes the following configuration. (Configuration 1) An exposure head having an organic light-emitting element, the organic light-emitting element includes a first electrode, a second electrode, an organic compound layer disposed between the first electrode and the second electrode, and a protective layer covering the second electrode; the organic compound layer has a light-emitting layer, An exposure head, wherein the number of peaks in the exposure spectrum emitted from the exposure head is greater than the number of peaks in the PL spectrum of the luminescent material contained in the luminescent layer. (Configuration 2) 2. The exposure head according to configuration 1, wherein the organic light-emitting element has an optical resonator structure formed by the first electrode and the second electrode. (Configuration 3) 3. The exposure head according to configuration 1 or 2, wherein the PL spectrum has two peaks. (Configuration 4) 4. The exposure head according to configuration 3, wherein the exposure spectrum has five or more peaks.

[0160] (Configuration 5) the organic compound layer further includes a first organic compound layer located between the first electrode and the light-emitting layer, and a second organic compound layer located between the light-emitting layer and the second electrode, the first electrode is a reflective electrode, and the second electrode is a light extraction electrode; 5. The exposure head according to any one of configurations 1 to 4, wherein the thickness of the first organic compound layer is smaller than the thickness of the second organic compound layer. (Configuration 6) The exposure head described in configuration 5, characterized in that the longest peak wavelength in the optical absorption spectrum of the second organic compound layer is farther from the maximum emission peak wavelength of the PL spectrum than the longest peak wavelength in the optical absorption spectrum of the first organic compound layer. (Configuration 7) 7. The exposure head according to any one of configurations 1 to 6, wherein the protective layer contains silicon nitride. (Configuration 8) 8. The exposure head according to any one of configurations 1 to 7, wherein the protective layer has a layer having aluminum oxide on a layer having silicon nitride. (Configuration 9) 9. The exposure head according to any one of configurations 1 to 8, wherein the organic light-emitting element has a top-emission type element structure arranged on an opaque substrate.

[0161] (Configuration 10) a photosensitive member and an exposure head that exposes the photosensitive member; 10. An image forming apparatus, wherein the exposure head is the exposure head according to any one of configurations 1 to 9. (Configuration 11) 11. The image forming apparatus according to claim 10, wherein all peaks of the exposure spectrum overlap with the light absorption spectrum of the photosensitive member. (Configuration 12) the organic compound layer further includes a first organic compound layer located between the first electrode and the light-emitting layer, and a second organic compound layer located between the light-emitting layer and the second electrode, The image forming apparatus according to Structure 10 or 11, wherein the maximum emission peak wavelength of the PL spectrum is closer to the maximum absorption peak wavelength in the visible light region of the light absorption spectrum of the photoreceptor than the longest peak wavelength in the light absorption spectrum of the first organic compound layer or the longest peak wavelength in the light absorption spectrum of the second organic compound layer. (Configuration 13) The image forming apparatus according to Configuration 12, wherein the maximum emission peak wavelength of the exposure spectrum is closer to the maximum absorption peak wavelength in the visible light region of the light absorption spectrum of the photosensitive member than the longest peak wavelength in the light absorption spectrum of the first organic compound layer and the longest peak wavelength in the light absorption spectrum of the second organic compound layer. [Explanation of symbols]

[0162] 1: substrate, 2: anode, 3: hole injection layer, 4: hole transport layer, 5: light emitting layer, 6: first electron transport layer, 7: second electron transport layer, 8: electron injection layer, 9: cathode, 10: first protective layer, 11: second protective layer, 12: third protective layer 40: PL spectrum of the luminescent material, 41: exposure spectrum emitted from the exposure head, 42: light absorption spectrum of the photoreceptor, 43: light absorption spectrum of the first organic compound layer, 44: light absorption spectrum of the second organic compound layer

Claims

1. An exposure head having an organic light-emitting element, the organic light-emitting element includes a first electrode, a second electrode, an organic compound layer disposed between the first electrode and the second electrode, and a protective layer covering the second electrode; the organic compound layer has a light-emitting layer, An exposure head, wherein the number of peaks in the exposure spectrum emitted from said exposure head is greater than the number of peaks in the PL spectrum of the luminescent material contained in said luminescent layer.

2. 2. The exposure head according to claim 1, wherein the organic light emitting element has an optical resonator structure formed by the first electrode and the second electrode.

3. 3. The exposure head according to claim 1, wherein the PL spectrum has two peaks.

4. 4. The exposure head according to claim 3, wherein the exposure spectrum has five or more peaks.

5. the organic compound layer further includes a first organic compound layer located between the first electrode and the light-emitting layer, and a second organic compound layer located between the light-emitting layer and the second electrode, the first electrode is a reflective electrode, and the second electrode is a light extraction electrode; 3. The exposure head according to claim 1, wherein the thickness of the first organic compound layer is smaller than the thickness of the second organic compound layer.

6. 6. The exposure head according to claim 5, wherein the longest peak wavelength in the optical absorption spectrum of the second organic compound layer is farther from the maximum emission peak wavelength of the PL spectrum than the longest peak wavelength in the optical absorption spectrum of the first organic compound layer.

7. 3. The exposure head according to claim 1, wherein the protective layer contains silicon nitride.

8. 3. The exposure head according to claim 1, wherein the protective layer comprises a layer having aluminum oxide on a layer having silicon nitride.

9. 3. The exposure head according to claim 1, wherein the organic light emitting element has a top emission type element structure arranged on an opaque substrate.

10. a photosensitive member and an exposure head that exposes the photosensitive member; 3. An image forming apparatus, wherein the exposure head is the exposure head according to claim 1.

11. 11. The image forming apparatus according to claim 10, wherein all peaks of the exposure spectrum overlap with the light absorption spectrum of the photosensitive member.

12. the organic compound layer further includes a first organic compound layer located between the first electrode and the light-emitting layer, and a second organic compound layer located between the light-emitting layer and the second electrode, 11. The image forming apparatus according to claim 10, wherein the maximum emission peak wavelength of the PL spectrum is closer to the maximum absorption peak wavelength in the visible light region of the light absorption spectrum of the photoreceptor than the longest wavelength peak wavelength in the light absorption spectrum of the first organic compound layer or the longest wavelength peak wavelength in the light absorption spectrum of the second organic compound layer.

13. 13. The image forming apparatus according to claim 12, wherein the maximum emission peak wavelength of the exposure spectrum is closer to the maximum absorption peak wavelength in the visible light region of the light absorption spectrum of the photosensitive member than the longest peak wavelength in the light absorption spectrum of the first organic compound layer and the longest peak wavelength in the light absorption spectrum of the second organic compound layer.

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