JP5658598B2 - Print head - Google Patents

Description

  Embodiments described herein relate generally to a print head and an image forming apparatus using an organic electroluminescence element (hereinafter referred to as an organic EL element) as a light source.

  In recent years, a print head using an organic EL element as a light source and an image forming apparatus using the print head have been developed.

  However, in the above-described print head, a transparent member such as glass or resin is used for a substrate or a sealing material in order to extract light from the light emitting element. The dust and dust adhere to the glass substrate and the sealing material, which are transparent members, obstruct the optical path, reduce the exposure amount, and cause defective images such as insufficient density and uneven density.

JP 2007-214252 A

  SUMMARY OF THE INVENTION Problems to be solved by the present invention include a print head that prevents adhesion of dust and dust such as toner in the machine body and a stable exposure amount, and is less likely to cause uneven density, and an image forming apparatus including the print head Is in the provision of.

In order to achieve the above object, a print head according to the present invention includes a holder, an erecting equal-magnification imaging rod lens array fixed to the holder, and the holder holding the rod lens array at a predetermined distance. A substrate that is fixed to the substrate, a layer that includes an antistatic member provided on the surface of the rod lens array on the surface of the substrate, and a surface that is opposite to the layer that includes the antistatic member. And a light source including an organic electroluminescence element that emits light to the rod lens array side through a substrate .

1 is a block diagram showing a configuration of an image forming unit of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an external perspective view showing the entire print head according to the embodiment. FIG. 3 is a cross-sectional view of the print head according to the present embodiment. Sectional drawing of the light emission part of the print head which uses the organic EL element of a bottom emission type. The top view of the board | substrate which has arrange | positioned the organic EL element to linear form. The top view of the board | substrate which has arrange | positioned the organic EL element in zigzag form. Sectional drawing of the light emission part of the print head which uses an organic electroluminescent element of a top emission type.

(This embodiment)
Hereinafter, embodiments of the present invention will be described with reference to FIGS.

  FIG. 1 is a diagram of an image forming unit when an embodiment of the present invention is applied to an image forming apparatus. The image forming unit is supported and stretched by a pair of rotating conveying rollers 1, a belt-shaped transfer medium 2, a print head 3, a developing roller 4 that supplies toner to a developing position, light emitted from the print head 3 and a developing roller 4, a photosensitive drum 5 on which an image is formed by the toner supplied from the toner 4, a charging charger 6 for applying charge to the photosensitive drum 5, a transfer roller 7 for transferring an image to a transfer medium, and a cleaner for removing unnecessary toner. 8 is provided.

  In FIG. 1, four sets of the image forming unit described above are provided. This is provided corresponding to each color in order to form a color image (yellow, magenta, cyan, black). Therefore, only one set of units has been described.

  FIG. 2 is an external perspective view of the print head 3 shown in FIG. The print head 3 includes a holder 9 in which a light emitting unit (organic EL element) is stored and a lens array 10 through which light from the light emitting unit passes.

  FIG. 3 is a sectional view of the print head 3 shown in FIG. A holder 9 and a rod lens array 10 for erecting equal-magnification imaging are provided. A light-emitting unit 11 is held and accommodated in the holder 9, and a lid 12 that covers the holder 9 is further provided. The rod lens array 10 is fixed to the holder 9 while maintaining a predetermined distance from the light emitting unit 11. In addition, a space 13 is provided to secure an optical path from the light emitting unit 11. Further, the holder 9 is fixed in the image forming apparatus so that the distance between the rod lens array 10 and the photosensitive drum 4 is a predetermined distance. The light emitting unit 11 includes a substrate 14, a thin film transistor (hereinafter referred to as TFT) 15, an anode 16, a light emitting layer 17, and a cathode 18.

  FIG. 4 is a diagram showing an example of the light emitting unit 11 of the bottom emission type print head according to the embodiment of the present invention. The light-emitting portion of this print head is sealed on a glass or resin substrate 14 via a TFT 15 to seal the anode 16, the light-emitting layer 17, the cathode 18, and the anode 16, the light-emitting layer 17 and the cathode 18. It is composed of a substrate 19. Each of the anode 16, the light emitting layer 17, and the cathode 18 constitutes each light emitting element (hereinafter referred to as “organic EL element”) shown in FIG. 5. In addition, an antistatic layer 20 made of an antistatic member is provided on the lower surface (corresponding to the upper surface in FIG. 3) of the substrate 14 serving as a light emission surface. This antistatic layer is a coating layer provided by coating a silicon resin or a fluororesin to which a surfactant such as glycerin fatty acid ester is added. Alternatively, an antistatic film made of a PET (polyethylene terephthalate) resin or the like to which a surfactant is added may be attached to the substrate using an acrylic pressure-sensitive adhesive that can be adhered uniformly without gaps while maintaining transparency. . The direction in which light is emitted from the light emitting unit 11 of such a print head is represented by a broken line block arrow. In this bottom emission type, it is possible to use a getter agent for preventing the cathode from getting wet with water, and the design is easy.

  Hereinafter, the light emission mechanism of the organic EL element of the print head shown in FIG. 4 will be described.

  An organic EL element serving as a light emitting source includes an anode 16 that is a transparent metal thin film such as ITO (indium tin oxide), a light emitting layer 17, and a cathode 18 that is a metal thin film such as aluminum, silver / magnesium alloy, or calcium. . As shown in this figure, an anode 16 that is an electrode for injecting holes, a cathode 18 that is an electrode for injecting electrons, and a light emitting layer 17 made of an organic material between the anode 16 and the cathode 18. It is sandwiched. When a direct current voltage or direct current is applied with the anode 16 as a positive electrode (+ electrode) and the cathode 18 as a negative electrode (−electrode), holes are injected into the light emitting layer 17 from the anode 16 and electrons are emitted from the cathode 18. Injected. In the light emitting layer 17, 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 anode 16 is a transparent metal thin film, the emitted light and the light reflected from the cathode 18 are emitted through the anode 16, the substrate 14 and the antistatic layer 20.

  The TFT 15 is a transistor as a switching element. In many cases, a plurality of TFTs 15 are attached to one organic EL element 21 (see FIG. 5) including the anode 16, the light emitting layer 17, and the cathode 18, and the light emission luminance is controlled. Further, the antistatic member prevents the adhesion of dust and dust by setting the surface resistance of the surface of the antistatic layer 20 to 10 ^ 6 to 10 ^ 14 Ω / sq.

  Garbage floating in the air, or dust or dirt, carries either positive or negative static electricity. For this reason, positively charged dust or dust is attracted to negatively charged substances and vice versa. In the atmosphere, there are a myriad of dust and dirt that are positively and negatively charged, and they adhere to all charged substances.

  Since glass, resin, and the like are insulators, the electric charge charged on the surface cannot be discharged by grounding such as ground or ground to remove the potential. Therefore, when the metal, which is a conductor, is brought into contact with glass or resin and grounded, electric charges charged on the glass or resin cannot be released.

  Accordingly, it is necessary to process and treat an insulator such as glass or resin so as not to be charged. In this embodiment, as described above, the antistatic layer 20 is provided on the surface to prevent charging.

  FIG. 5 is a top view (viewed from the light emission side) of the substrate 14 of the print head that uses an organic EL element in the light emitting section. An EL element 21 is disposed. Here, for example, in the case of a head corresponding to image formation of A3 size with a resolution of 1200 dpi in the main scanning direction, the organic EL elements 21 are arranged in a straight line at intervals of approximately 21 μm (= 25.4 mm / 1200), for a total of 15,360. Individually arranged. As shown in FIGS. 1 and 2, the head using an organic EL as a light source does not need a movable part like a laser scanning unit having a polygon motor, and is arranged on the head substrate with high definition. Since a rod lens array capable of forming an image of a light emitting element on a photosensitive member at an equal magnification is used, the size and thickness can be reduced.

  In order to ensure higher resolution, the organic EL elements 21 may be arranged in two rows in a staggered manner as shown in FIG. When arranged in a staggered manner, the resolution can be improved by a factor of two. In addition, since the area of the light emitting element can be increased without changing the resolution, the applied current can be increased and the amount of emitted light can be increased.

  In this embodiment, as shown in FIG. 7, it is possible to configure a print head using a top emission type organic EL element. In the figure, light emitted from the light emitting layer 17 passes through the cathode 18 in the direction indicated by the broken line block arrow, passes through the transparent sealing substrate 19 formed of glass, resin, or the like, and passes through the antistatic layer 20. Through the device. The cathode 18 is made of ITO, which is a transparent thin film normally used for the anode in the bottom emission type. However, a thin film of magnesium or lithium is attached to the interface of the ITO to increase the efficiency of electron injection. Used as cathode. Also in this case, if charged dust or dirt adheres to the sealing substrate in contact with the outside of the element, the amount of light is reduced or uneven, so an antistatic measure (antistatic layer 20) is provided on the surface of the sealing substrate 19. It is necessary to take.

  In the case of the bottom emission type print head shown in FIG. 4, since the light from the light emitting portion passes through the TFT 16, the aperture ratio is limited and high definition cannot be achieved. However, since this top emission type does not go through the TFT 15, it is possible to obtain a high aperture ratio. Therefore, high definition can be achieved. Also in this case, adhesion of toner or the like can be prevented by providing the antistatic layer 20 of the antistatic member on the outer surface of the sealing substrate 19.

  As described above, by adopting the configuration as shown above, a print head that prevents dust and dust such as toner in the machine body from adhering and obtains a stable exposure amount and is less likely to cause uneven density, and an image forming apparatus including the print head are provided. Can be provided. In addition, since the substrate or the sealing member on which the antistatic layer is applied is a flat surface, the optical characteristics are hardly distorted. Therefore, even when compared with other print heads, it is possible to prevent the occurrence of optical unevenness. In addition, since light emission efficiency is improved, power consumption can be reduced.

  As described above, according to the present embodiment, it is possible to provide an image forming apparatus that uses a small-sized organic EL head with low driving power and does not deteriorate image quality due to adhesion of dust, dust, and the like.

  As mentioned above, although embodiment of this invention was described, this embodiment is shown as an example and is not intending limiting the range of 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 1 ... Conveyance roller 2 ... Transfer belt 3 ... Print head 4 ... Development roller 5 ... Photosensitive drum 6 ... Development roller 7 ... Transfer roller 8 ... Cleaner 14 ... Substrate 15 ... TFT
16 ... anode 17 ... light emitting layer 18 ... cathode

Claims (5)

A holder,
A rod lens array for erecting equal magnification imaging fixed to this holder,
A substrate that is fixed to the holder while maintaining a predetermined distance from the rod lens array;
A layer containing an antistatic member provided on the surface of the substrate on the rod lens array side ;
A light source including an organic electroluminescence element that is formed on the side opposite to the layer containing the antistatic member and emits light to the rod lens array side through the substrate ;
A print head comprising: The print head according to claim 1, wherein the layer containing the antistatic member is a coating layer. 2. The print head according to claim 1, wherein the surface resistance of the antistatic member is 10 ^ 6 to 10 ^ 14 Ω / sq. The print head according to claim 1, wherein the substrate is a glass substrate that transmits light. The print head according to claim 1, wherein the substrate is a resin substrate that transmits light.

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