JP2013111926A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that has higher picture quality.SOLUTION: The image forming apparatus includes: an exposure portion which emits light from a plurality of arrayed organic EL elements; a photoreceptor which is arranged having an inner peripheral surface nearby or in contact along an outer peripheral surface side of the exposure portion while curved concentrically and substantially to the curvature of the exposure portion, and has a latent image formed on its surface with the light emitted from the exposure portion; and an image forming portion which forms an image on a recording medium based upon the latent image.

Description

  Embodiments described herein relate generally to an image forming apparatus.

  In a conventional image forming apparatus, as an exposure method for writing a latent image on a photoreceptor, a laser beam method using a semiconductor laser as a light source or an LED array method using an LED array in which a plurality of inorganic LEDs are arranged on a line is used. There is a device used.

  The image forming apparatus having this structure often uses an LED as a light source of the photosensitive drum. However, the focal length varies depending on the variation in the distance from the LED to the surface of the photosensitive drum caused by the variation in the height of the LED chip. There is a risk that it will not match the surface of the drum. Further, there is an image forming apparatus that uses an organic electroluminescence element (organic EL light emitting element) as a light source, although it is not bent concentrically with the curvature of the photosensitive drum.

JP 2004-195788 A

  The problem to be solved by the present invention is to provide an image forming apparatus that prevents variations in the distance from the light source to the photoconductor, and has a focal length that matches the surface of the photoconductor.

  In order to solve the above-described problem, an image forming apparatus according to an embodiment includes an exposure unit that emits light by a plurality of organic EL elements arranged, and an inner periphery that is curved substantially concentrically with a curvature of the exposure unit. A photoconductor having a surface close to or in contact with the outer peripheral surface of the exposure unit and forming a latent image on the surface by light emitted from the exposure unit, and forming an image on a recording medium based on the latent image And an image forming unit.

1 is a schematic configuration diagram showing an MFP equipped with a photosensitive drum according to an embodiment. 1 is a schematic configuration diagram showing a printer equipped with a photosensitive drum according to an embodiment. It is explanatory drawing which shows the cross section of the photoreceptor drum used for the image forming apparatus of this embodiment. FIG. 3 is an explanatory diagram illustrating a configuration for one pixel of the photosensitive drum according to the exemplary embodiment. Explanatory drawing which shows the exposure head of this embodiment. It is a figure which shows the light emitting element of this embodiment, (a) is explanatory drawing when a light emitting element is arrange | positioned in 1 row, (b) is explanatory drawing when a light emitting element is arrange | positioned in zigzag form. is there. The equivalent circuit schematic of the organic electroluminescent light emitting device of this embodiment.

  Hereinafter, an embodiment for carrying out the invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram illustrating a color MFP (Multi Functional Peripheral) 1 that is an image forming apparatus. The MFP 1 includes an image forming unit 2 and a paper feeding unit 3 that supplies the image forming unit 2 with paper P as a fixing medium. The MFP 1 further includes an automatic document feeder 4 and a scanner unit 5 that reads the document D supplied by the automatic document feeder 4 on the upper surface. The image forming unit 2 is provided with a registration roller 7.

  The sheet feeding unit 3 includes a cassette 9 that stores sheets P stacked in a stacked manner, and a pickup roller 10 that feeds the uppermost sheet of the sheets P stored in the cassette 9 to the image forming unit 2.

  The image forming unit 2 includes four image forming stations 30Y, 30M, 30C, and 30K of Y (yellow), M (magenta), C (cyan), and K (black), and the image forming stations 30Y, 30M, and 30C. , 30K, and the like, and an intermediate transfer belt 32 for transferring the toner image formed by 30K. The image forming unit 2 includes a fixing device 33.

  FIG. 2 is a schematic configuration diagram showing a monochrome printer as an image forming apparatus. A monochrome printer 6 shown in FIG. 2 includes an image forming unit 2 and a scanner unit 5. The mechanism of the image forming unit 2 will be described. The image forming unit 2 includes a charging charger 12 that uniformly charges the photosensitive drum 11 around the photosensitive drum 11, and a latent image created on the charged photosensitive drum 11 based on image data from the scanner unit 5. A developing unit 13 for developing the toner, a transfer charger 14 for transferring the image developed on the photosensitive member 11 to the paper P, a peeling charger 15, and a cleaner 16 for cleaning the current agent remaining on the photosensitive drum 11. The charging charger 12, the developing device 13, the transfer charger 14, the peeling charger 15, and the cleaner 16 are sequentially arranged according to the rotation direction of the arrow A of the photosensitive drum 11. Further, the image forming unit 2 includes an exposure head 17 using an organic electroluminescence element (organic EL light emitting element) inside the photosensitive drum 11.

  The image forming unit 2 is provided with a path 21 including a transport belt 20 that transports the paper P on which the toner image has been transferred in order downstream from the peeling charger 15 in the paper transport direction, and a paper discharge transport guide 21. The image forming unit 2 includes a fixing device 22 that sequentially fixes the paper P to the downstream side in the paper transport direction from the paper discharge transport guide 21 and a paper discharge roller 24.

  Next, an image forming process operation will be described.

  The electrostatic latent image formed on the photosensitive drum 11 is developed with toner (developer) supplied from the developing device 13. The photosensitive drum 13 on which the toner image is formed transfers the electrostatic latent image onto the paper P by the transfer charger 14.

  The photosensitive layer 18 that has been transferred to the sheet is returned to the initial state after the residual toner on the surface thereof is removed by the cleaner 16, and enters a standby state for the next image formation.

  By repeating the above process operation, the image forming operation is continuously performed.

  Next, the periphery of the photosensitive drum 11 will be described with reference to FIGS.

  As shown in FIG. 3B, the photosensitive layer 18 has a three-layer structure in which a drum-shaped translucent support 18a is the innermost layer. A translucent conductive layer 18b is laminated on the translucent support 18a, and a photoconductor layer 18c is further laminated. The translucent support 18a, the translucent conductive layer 18b, and the photoconductor layer 18c are all light transmissive.

  The translucent support 18a is preferably transparent or translucent, and examples thereof include glass, quartz, and resin (plastic and plastic film).

  An exposure head 17 is disposed inside the photosensitive layer 18. The exposure device 17 is disposed inside the photosensitive drum 11 between the charging charger 12 and the developing device 13. The curvature of the portion of the exposure apparatus 17 that contacts the translucent support 18a is the same as the curvature inside the translucent support 18a. The exposure device 17 may be provided on the entire inner peripheral surface of the photosensitive drum 11 and may rotate with the rotation of the photosensitive drum 11. Further, the exposure device 17 may be disposed only between the charging charger 12 and the developing device 13 and may be fixed without rotating together when the photosensitive drum 11 rotates.

  A detailed configuration of the exposure head 17 will be described with reference to FIG. As the structure of the organic EL light emitting element, a bottom emission type that extracts light generated from the light emitting layer from the substrate side (bottom emission type) and a top emission type that extracts light generated from the light emitting layer to the outside of the device from the side opposite to the substrate side (Top emission type). Either a bottom emission type or a top emission type may be used, but in FIG. 4, an example of a bottom emission type organic EL light emitting element will be described.

  The exposure head 17 includes a substrate 30, a thin film transistor (hereinafter referred to as TFT) 52, an anode 70, an organic EL emitter array 50 that is a light emitting layer, a cathode 71, and a sealing member 53. Yes. The substrate 30 is disposed on the outermost curved surface, and the thin film transistor 52 is disposed on the inner side in contact with the substrate 30.

  That is, the photosensitive TFT lighting circuit array 52 having the same curvature as that of the translucent support 18a is formed on the inner peripheral surface of the translucent support 18a of the photosensitive layer 18, and the organic EL light emitter is further formed on the inner peripheral surface thereof. An array 50 is formed. At this time, the centers of the translucent support 18a and the photosensitive TFT lighting circuit array 52 are concentric. Further, a sealing substrate 30 for sealing them is provided.

  The organic EL light emitter array 50 has an anode 70 and a cathode 71 disposed on both sides. Both ends of the anode 70 are in contact with the organic EL light emitter array 50, but the central portion of the anode 70 is not in contact with the organic EL light emitter array 50.

  The TFT circuit array 52 is made of, for example, low-temperature polysilicon or amorphous silicon and has a very small thickness. Furthermore, the accuracy is very high. For this reason, the variation in the distance from the organic EL light emitter array 50 to the photosensitive member is extremely small, and the variation in the focal length is also small, so that high-definition exposure is possible.

  Further, since the space of the TFT circuit reduces the light emission area ratio and the aperture ratio of each pixel, the rod lens array and the micro lens array that are essential for the photosensitive drum 11 including the organic EL light emitting element 51 as a surface light source. A high-definition image can be formed without a focusing means such as the above.

  The organic EL light emitter array 50 is formed by vapor deposition or coating, for example, is a nano-order thin film, and has very high accuracy. For this reason, the variation in the distance from the organic EL light emitter array 50 to the photosensitive member is extremely small, and the variation in the focal length is also small, so that high-definition exposure is possible.

  The organic EL light emitter array 50 has a configuration in which an anode 70 that injects holes, a cathode 71 that is an electrode that injects electrons, and an organic EL light emitter array 50 made of an organic material are in contact with both electrodes. is there. When a direct current voltage or direct current is applied with the anode 70 as a positive electrode (+ electrode) and the cathode 71 as a negative electrode (−electrode), holes are injected from the anode 70 into the organic EL light emitter array 50 and from the cathode 71. Are injected with electrons. In the organic EL light emitter array 50, a light emission phenomenon occurs when excitons generated by recombination of injected holes and electrons shift from the excited state to the ground state. Since the electrode of the anode 70 is a transparent electrode such as ITO (indium tin oxide), the emitted light and the light reflected from the cathode 71 are emitted through the anode 70 and the substrate 30.

  The exposure head 17 disposed inside the photosensitive layer 18 will be described with reference to FIGS. 5 and 6A and 6B.

  The exposure head 17 is formed with a curvature substantially equal to the inner peripheral surface of the photosensitive layer 18. By arranging a plurality of organic EL light emitting elements 51 along the longitudinal direction of the photosensitive layer 18, an organic EL light emitting array 50 that is a line-shaped light emitting portion is formed. The light emission direction of the organic EL light emitter array 50 is configured to face the outer peripheral side of the photosensitive layer 18.

  As shown in FIG. 6A, for example, if the organic EL light emitting array 50 is a head corresponding to image formation of A3 size having a resolution of 1200 dpi in the main scanning direction, the organic EL light emitting element 51 is approximately 21 μm (= 25). .4 mm / 1200) intervals, a total of 15,360 are arranged on a straight line.

  The wiring structure of the exposure head 17 will be described with reference to the equivalent circuit diagram of FIG. A plurality of gate lines 60, a plurality of signal lines 61 extending in a direction intersecting the gate lines 60, and a plurality of power supply lines 62 extending in parallel to the signal lines 61 are provided. The light emitting element region S corresponds to a region surrounded by the gate line 60 and the signal line 61.

  The signal line 61 is connected to a data side drive circuit 63 including a shift register, a level shifter, a video line, and an analog switch. The gate line 60 is connected to a scanning side drive circuit 64 including a shift register and a level shifter. Each of the light emitting element regions S includes a switching thin film transistor 65 to which a scanning signal is supplied to the gate via the gate line 60, and a holding capacitor cap 66 for holding a pixel signal supplied from the signal device 61 via the switching TFT 65. A driving TFT 67 to which the pixel signal held by the holding capacitor cap 66 is supplied to the gate, an anode 70 into which a driving current flows from the power line 62 when electrically connected to the power source 68 via the driving TFT 67, and An organic EL light emitter array 50 sandwiched between an anode 70 and a cathode 71 is provided. An element constituted by the anode 70, the cathode 71 and the organic EL light emitter array 50 is an organic EL light emitting element 51.

  In the above circuit configuration, when the switching TFT 65 is turned on by the drive signal supplied from the gate line 60, the potential of the signal line 61 at that time is held in the holding capacitor cap66, and the state of the holding capacitor cap66 is changed. Thus, the on / off state of the driving TFT 67 is controlled. A voltage is applied from the power supply line 62 to the anode 70 via the channel of the driving TFT 67, and a current flows between the cathode 71. The organic EL light emitter array 50 emits light according to this amount of current.

  In the organic EL light emitter array 50, the organic EL light emitting elements 51 may be arranged in a staggered manner as shown in FIG. When the organic EL light emitting elements 51 are arranged in a staggered manner, the resolution can be improved by a factor of two. In addition, since the area of the organic EL light emitting element 51 can be increased without changing the resolution, the applied current can be increased and the amount of emitted light can be increased.

  According to the embodiment described above, since the exposure head 17 and the photoconductor layer 18c of the photosensitive layer 18 are disposed close to each other, high-definition exposure can be performed without using an optical system such as a rod lens array or a microlens array. Is possible.

  In addition, since the space of the TFT circuit portion can reduce the light emitting area ratio and the aperture ratio, higher-definition exposure is possible.

  Furthermore, a small and high-quality image forming apparatus can be provided.

  The present invention is not limited to the above embodiment, and various modifications can be made. In the present embodiment, the organic EL light emitting element has been described as being a bottom emission type, but may be a top emission type. The top emission type is an organic EL light emitting element that extracts light generated from the light emitting layer from the side opposite to the substrate.

  A top emission type organic EL light emitting device is formed on a substrate in the order of a reflective layer, an anode, a hole injection layer, a light emitting layer, a cathode, and a sealing layer. The light emitting layer is disposed between the anode and the cathode.

  The reflective layer is formed with a thickness of about 150 nm on the substrate surface. The reflective layer reflects light from the light emitting layer toward the light emitting layer. As the material of the reflective layer, for example, Al, Ag, Mo, W, Ni, Cr or the like is used.

  In addition, when a top emission type organic EL light emitting element is used, since the emitted light is extracted from the sealing substrate side which is the opposite side of the substrate, the substrate may not transmit light. Examples of the opaque substrate include a thermosetting resin and a thermoplastic resin in addition to a ceramic sheet such as alumina and a metal sheet such as stainless steel that has been subjected to an insulation treatment such as surface oxidation. Further, the anode does not have to be light transmissive.

  Although an embodiment of the present invention has been described, this embodiment is presented as an example and is not intended to limit the scope of the invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 11 ... Photosensitive drum 17 ... Exposure head 18 ... Photosensitive layer 30 ... Substrate 50 ... Organic EL light emitter array 70 ... Anode 71 ... Cathode

Claims (3)

An exposure unit that emits light by a plurality of organic EL elements arranged;
In a state where the curvature is approximately concentric with the curvature of the exposure portion, an inner peripheral surface is disposed close to or in contact with the outer peripheral surface side of the exposure portion, and a latent image is formed on the surface by light emitted from the exposure portion. A photoreceptor to be formed;
An image forming apparatus comprising: an image forming unit that forms an image on a recording medium based on the latent image. The exposure unit is
A transparent substrate on which a thin film transistor is formed;
An anode bonded to the thin film transistor;
A light emitter by the organic EL element joined to the anode;
A cathode bonded to the organic EL element;
The image forming apparatus according to claim 1, comprising: The image forming unit includes a charging charger and a developing device,
2. The outer peripheral surface of the photosensitive member at a portion where the outer peripheral surface of the exposure unit and the inner peripheral surface of the photosensitive member are close to or in contact with each other is located only between the charging charger and the developing device. Image forming apparatus.

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