JP2006231649A - Optical head and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head in which a ghost spot is not formed on an image carrier, and an image forming apparatus. <P>SOLUTION: The apparatus comprises the image carrier 20, an electrifying means 22, an image writing means 23 consisting of an organic EL array exposure head, and a case 50 covering the image writing means 23. An opening 51 which brings a developing means into contact is provided on the case 50. Masking parts 52 and 53 of the case 50 are left between the opening 51 and the image writing means 23. Flange parts 52a and 53a are provided on ends of the masking parts 52 and 53. A light guiding slit 84 is formed between the flange parts 52a and 53a so as to project only an outputting light of a light emitting part 63 on an image face. A straying light is masked by the flange parts 52a and 53a. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical head in which a ghost spot is not formed on an image carrier and an image forming apparatus.

  In general, an electrophotographic toner image forming unit includes a photosensitive member as an image bearing member having a photosensitive layer on an outer peripheral surface, a charging unit that uniformly charges the outer peripheral surface of the photosensitive member, and a uniform charging unit using the charging unit. An exposure unit that selectively exposes the outer peripheral surface charged to form an electrostatic latent image, and a toner as a developer is applied to the electrostatic latent image formed by the exposure unit to form a visible image ( Developing means for forming a toner image).

  As a tandem type image forming apparatus for forming a color image, a plurality of (for example, four) toner image forming units as described above are arranged on an intermediate transfer belt, and a photoconductor using these monochromatic toner image forming units. The upper toner images are sequentially transferred to the intermediate transfer belt, and a plurality of color (for example, yellow, cyan, magenta, black) toner images are superimposed on the intermediate transfer belt to obtain a color image on the intermediate transfer belt. There is an intermediate transfer belt type.

  In the tandem image forming apparatus as described above, an optical head including an LED array or an organic EL array may be used as an exposure unit. For example, Patent Document 1 describes a light emitting element array in which LED light emitting elements are integrated on a single chip.

  An example of an optical head that uses an organic EL light emitting element as a light source and forms an image on an image carrier by a rod lens array optical system will be described. FIG. 8 is a sectional view of the optical head (image writing means) 23 in the sub-scanning direction. The image writing means 23 is provided with a gradient index rod lens array (SLA) 65. Reference numeral 81 denotes a rod lens, and the rod lens array 65 is attached to an opaque housing 60. An organic EL light emitting element array 61 is attached facing the rear surface of the gradient index rod lens array 65 in the housing 60.

  The organic EL light emitting element array 61 in the housing 60 is shielded from the rear surface of the housing 60 by an opaque cover 66. 63 is a light emitting part (organic EL light emitting element), and 64 is a cover glass. The cover 66 is pressed against the back surface of the housing 60 by a fixed leaf spring 67 to seal the inside of the housing 60 in a light-tight manner. The housing 60 covers the periphery of the glass substrate 62 and the side facing the image carrier 20 is open. In this way, the light emitted from the light emitting unit 63 is projected onto the image carrier 20 through the rod lens 81.

JP-A-11-138899

  In the optical head as shown in FIG. 8, a ghost spot 93 may be generated on the image carrier 20. Next, the reason will be described. When forming the organic EL light emitting element 63, an anode or a cathode is used. Since the cathode is made of Al or the like, it becomes a mirror and reflects stray light in the light emitting element substrate. Therefore, a ghost spot 93 is generated on the image carrier 20 when the reflected light 95 passes through the rod lens 81.

  FIG. 9 is a plan view of the image carrier 20 transmitted from the SLA 65 side in FIG. In FIG. 9, 91 and 92 are exposure spots formed on the image carrier 20 by the organic EL light emitting element 63, CL is a center line of the SLA 65, and 93 and 94 are ghost spots. The ghost spot includes a large ghost spot 93 formed concentrically with each rod lens 81 and a small ghost spot 94 generated near the boundary between the rod lenses 81. The formation of such ghost spots 93 and 94 on the image carrier 20 has a problem that the print quality is deteriorated.

  The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide an optical head in which a ghost spot due to stray light is not formed on an image carrier, and an image forming apparatus using the same. It is to provide.

  An optical head of the present invention that achieves the above object includes a light-transmitting substrate, an organic EL light-emitting element formed on the substrate, and a lens array optical system, and is arranged on an image carrier by the lens array optical system. In the optical head for forming an image, a shielding means for preventing stray light from being projected onto the image carrier is provided. According to this configuration, a ghost spot due to stray light is not formed on the image carrier, so that print quality can be improved.

  In the optical head of the present invention, the shielding means is a cover that covers the image carrier, in which a light guide slit that projects only the output light of the organic EL light emitting element onto an image surface is formed. And In this way, the image carrier is covered with a cover in which light guide slits are formed, so that ghost spots due to stray light are not formed on the image carrier, thereby preventing image unevenness and printing. Quality can be improved.

  In the optical head of the present invention, the stray light shielding means covers the lens array optical system and is provided with an opening for projecting output light of the organic EL light emitting element onto an image plane. It is characterized by that. By attaching such a light guide cover, it is possible to prevent a ghost spot due to stray light from being formed on the image carrier with a simple configuration. Further, it can be used as an alignment member between the exposure position of the image carrier and the lens array. For this reason, it is possible to prevent the displacement of the lens array.

  In the optical head of the present invention, the light guide cover has a substantially truncated cone shape. For this reason, it is possible to prevent stray light from being projected onto the image carrier and to prevent scattered toner from adhering to the rod lens, thereby preventing the rod lens from being contaminated.

  In the optical head of the present invention, the substrate is a glass substrate. For this reason, light transmittance becomes favorable and light can be efficiently projected from the organic EL light emitting element to the image carrier.

  Further, the image forming apparatus of the present invention is provided with at least two or more image forming stations in which image forming units of the charging unit, any one of the optical heads, the developing unit, and the transfer unit are arranged around the image carrier, An image is formed by a tandem method by passing the transfer medium through each station. For this reason, in the tandem image forming apparatus, it is possible to prevent deterioration in print quality due to the formation of ghost spots.

  In addition, the image forming apparatus of the present invention includes an intermediate transfer member. For this reason, in the image forming apparatus provided with the intermediate transfer member, it is possible to prevent the deterioration of the print quality due to the formation of the ghost spot.

  According to the optical head and the image forming apparatus of the present invention, the shielding means for preventing the stray light from being projected onto the image carrier is provided. For this reason, since no ghost spot due to stray light is formed on the image carrier, the print quality can be improved.

  The present invention will be described below with reference to the drawings. FIG. 4 is a schematic cross-sectional view showing an example of an image forming apparatus to which the line head of the present invention is applied. In this embodiment, an intermediate transfer belt is used as the transfer belt. In FIG. 4, the image forming apparatus 1 of the present embodiment is mounted on a housing body 2, a first opening / closing member 3 that is openably / closably mounted on the front surface of the housing body 2, and on an upper surface of the housing body 2. The first opening / closing member 3 also has an opening / closing lid 3 ′ attached to the front surface of the housing body 2 so as to be openable and closable. The opening / closing lid 3 ′ can be opened and closed in conjunction with or independently of the first opening / closing member 3.

  In the housing body 2, an electrical component box 5 containing a power circuit board and a control circuit board, an image forming unit 6, a blower fan 7, a transfer belt unit 9, and a paper feed unit 10 are disposed, and a first opening / closing member In FIG. 3, a secondary transfer unit 11, a fixing unit 12, and a recording medium conveying means 13 are arranged. The consumables in the image forming unit 6 and the paper feeding unit 10 are configured to be detachable from the main body. In this case, the configuration including the transfer belt unit 9 can be removed and repaired or replaced. It is said.

  The transfer belt unit 9 is disposed below the housing body 2 and is driven to rotate by a drive source (not shown), a driven roller 15 disposed obliquely above the drive roller 14, and the two rollers. An intermediate transfer belt 16 that is stretched between 14 and 15 and driven to circulate in the direction of the arrow shown in the figure, and a cleaning means 17 that comes into contact with and separates from the surface of the intermediate transfer belt 16. In the example of FIG. 4, the driven roller 15 and the intermediate transfer belt 16 are disposed in a direction inclined to the left in the drawing with respect to the driving roller 14.

  A primary transfer member 21 made of a leaf spring electrode is opposed to an image carrier 20 of each image forming station Y, M, C, K described below on the back surface of the intermediate transfer belt 16 facing downward in the conveying direction. The transfer bias is applied to the primary transfer member 21 by contact with the elastic force. A test pattern sensor 18 is installed on the support frame 9 a of the transfer belt unit 9 in the vicinity of the drive roller 14. This test pattern sensor 18 is a sensor for positioning each color toner image on the intermediate transfer belt 16, detecting the density of each color toner image, and correcting the color shift and image density of each color image.

  The image forming unit 6 includes a plurality of (four in this embodiment) image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form images of different colors. The image forming stations Y, M, C, and K each include an image carrier 20 formed of a photosensitive drum, and a charging unit 22 and an optical head (image writing unit) disposed around the image carrier 20. ) 23 and developing means 24. Note that the charging unit 22, the image writing unit 23, and the developing unit 24 give the figure numbers only to the image forming station Y, and the other image forming stations have the same configuration, and thus the drawing numbers are omitted. Further, the arrangement order of the image forming stations Y, M, C, and K is arbitrary.

  The image carriers 20 of the respective image forming stations Y, M, C, and K are disposed so as to abut on the belt surface 16 a facing downward in the transport direction of the intermediate transfer belt 16. As a result, the image forming stations Y, M, C, and K are also arranged in a direction inclined to the left in the drawing with respect to the driving roller 14. The image carrier 20 is rotationally driven in the conveyance direction of the intermediate transfer belt 16 as indicated by the arrows in the figure. The intermediate transfer belt 16 is provided with a cleaning means 17 to collect the transfer residual toner.

  The charging means 22 is composed of a conductive brush roller connected to a high voltage generation source, and the outer periphery of the brush is opposite to the image bearing member 20 as a photosensitive member at a peripheral speed of 2 to 3 times. The surface of the image carrier 20 is uniformly charged by contact rotation. By using such a charging means 22, the surface of the image carrier can be charged with an extremely small current, so that the inside and outside of the apparatus is not contaminated with a large amount of ozone unlike the corona charging method. In addition, since the contact with the image carrier 20 is soft, it is difficult for the transfer residual toner generated when the roller charging method is used to adhere to the charging roller, and stable image quality and device reliability are ensured. can do.

  The image writing means 23 uses an organic EL array exposure head in which organic EL light emitting elements are arranged in a line in the axial direction of the image carrier 20. The organic EL array exposure head has an advantage that the optical path length is shorter than that of the laser scanning optical system, is compact, can be disposed close to the image carrier 20, and the entire apparatus can be downsized. In this embodiment, the image carrier 20, the charging unit 22 and the image writing unit 23 of each of the image forming stations Y, M, C and K are unitized as one image carrier unit 25 and supported together with the transfer belt unit 9. By making the frame 9a replaceable, the positioning of the organic EL array exposure head with respect to the image carrier 20 is maintained. In addition, when the image carrier unit 25 is replaced, the organic EL array exposure head is also replaced.

  Next, the configuration of the developing unit 24 will be described on behalf of the image forming station K. The developing unit 24 includes a toner storage container 26 that stores toner (hatched portion in the drawing), a toner storage part 27 formed in the toner storage container 26, and a toner stirring member disposed in the toner storage part 27. 29, a partition member 30 partitioned at the upper portion of the toner storage portion 27, a toner supply roller 31 disposed above the partition member 30, and abutment against the toner supply roller 31 provided on the partition member 30. The blade 32, the developing roller 33 disposed so as to be in contact with the toner supply roller 31 and the image carrier 20, and the regulation blade 34 being in contact with the developing roller 33. The image carrier 20 is rotated in the conveyance direction of the intermediate transfer belt 16, and the developing roller 33 and the supply roller 31 are driven to rotate in the direction opposite to the rotation direction of the image carrier 20 as shown by the arrows in the figure.

  Further, the paper feed unit 10 includes a paper feed unit including a paper feed cassette 35 in which the recording media P are stacked and held, and a pickup roller 36 that feeds the recording media P from the paper feed cassette 35 one by one. Yes. In the first opening / closing member 3, a registration roller pair 37 that defines the timing of feeding the recording medium P to the secondary transfer unit, and a secondary transfer unit that is pressed against the drive roller 14 and the intermediate transfer belt 16. A secondary transfer unit 11, a fixing unit 12, a recording medium conveyance unit 13, a paper discharge roller pair 39, and a duplex printing conveyance path 40 are provided.

  The fixing unit 12 includes a heating roller 45 that includes a heating element such as a halogen heater and is rotatable, a pressure roller 46 that presses and biases the heating roller 45, and is swingable on the pressure roller 46. The belt tension member 47, and the heat-resistant belt 49 stretched between the pressure roller 45 and the belt tension member 47, and the color image secondarily transferred to the recording medium are the heat roller 45 and the heat-resistant belt 49. The toner image is fixed on the recording medium at a predetermined temperature at the nip portion formed in step 1). In this embodiment, the fixing unit 12 can be disposed in a space formed obliquely above the intermediate transfer belt 16, in other words, in a space opposite to the image forming unit 6 with respect to the intermediate transfer belt 16. Thus, heat transfer to the electrical component box 5, the image forming unit 6, and the intermediate transfer belt 16 can be reduced.

  FIG. 5 is a schematic perspective view showing an example of the optical head (image carrier) 23 according to the embodiment of the present invention. FIG. 5 shows an example of a mechanism for accurately positioning the image writing unit 23 with respect to each image carrier (photosensitive drum) 20 attached to the image carrier unit 25. The image carrier 20 described with reference to FIG. 4 is rotatably attached to the case 50 of the image carrier unit 25 on its axis. The organic EL light emitting element array 61 is held in a long housing 60.

  Positioning pins 69 provided at both ends of the long housing 60 are fitted into opposing positioning holes of the case 50, and fixing screws are screwed into the screw holes of the case 50 through screw insertion holes 68 provided at both ends of the long housing 60. Each image writing means 23 is fixed at a predetermined position by screwing and fixing. Reference numeral 81 denotes a rod lens.

  FIG. 6 is a cross-sectional view of the image writing unit 23 in the main scanning direction. As shown in FIG. 6, the light beam output from the light emitting unit of the organic EL light emitting element array 61 passes through the glass substrate 62 and is emitted to the image carrier 20 side. And the glass substrate 62 is comprised by the surface where the surface where the said light emission part is formed, and the surface where a light ray injects are substantially parallel.

  FIG. 7 is a sectional view partially showing the optical head according to the embodiment of the present invention. FIG. 7 shows an example of the vicinity of the light emitting portion 63 of the organic EL light emitting element array 61 provided in the image writing means 23. The organic EL light emitting element array 61 is provided with a TFT (thin film transistor) 71 made of polysilicon having a thickness of 50 nm for controlling light emission of each light emitting portion 63 on a glass substrate 62 having a thickness of 0.5 mm, for example. As shown in FIG. 7, the TFT 71 is provided at a position that does not block the emitted light La, for example, corresponding to each of the two rows of light emitting units 63 in a staggered arrangement.

An insulating film 72 made of SiO ₂ having a thickness of about 100 nm is formed on the glass substrate 62 except for the contact hole on the TFT 71, and ITO having a thickness of 150 nm is connected to the TFT 71 through the contact hole. An anode 73 made of is formed. Next, another insulating film 74 made of SiO ₂ having a thickness of about 120 nm is formed in a portion corresponding to a position other than the light emitting portion 63.

  On the insulating film 74, a bank 75 made of polyimide having a thickness of 2 μm and having a hole 76 corresponding to the light emitting portion 63 is provided, and in the hole 76 of the bank 75, a thickness of 50 nm is sequentially formed from the anode 73 side. A hole injection layer 77 and a light emitting layer 78 having a thickness of 50 nm are formed. A cathode first layer 79a made of Ca having a thickness of 100 nm and a cathode second layer 79b made of Al having a thickness of 200 nm are sequentially formed so as to cover the upper surface of the light emitting layer 78, the inner surface of the hole 76, and the outer surface of the bank 75. Be filmed.

  On top of that, the light-emitting portion 63 of the organic EL light-emitting element array 61 is configured by being covered with a cover glass 64 having a thickness of about 1 mm via an inert gas 80 such as nitrogen gas. Light emission from the light emitting unit 63 is performed on the glass substrate 62 side. The outgoing lights La and Lb from the light emitting layer 78 are projected onto the image carrier through the rod lens. Thus, in this invention, since the organic EL light emitting element is formed on the glass substrate, the light transmittance is improved. In addition, a light-emitting element can be easily manufactured. Furthermore, since the shape of the light-emitting element can be set to an arbitrary shape, cost can be reduced.

  When the light emitting unit 63 operates to emit light, stray light is generated due to various factors in addition to the normal emitted lights La and Lb emitted in the direction of the image carrier. As described above, the cathode second layer 79b is made of a metal having high reflectance such as Al. For this reason, part of the stray light is reflected by the cathode second layer 79b, passes through the glass substrate 62, and forms a ghost spot on the image carrier through the rod lens.

  In the embodiment of the present invention, the optical head is configured so that such a ghost spot is not formed on the image carrier. An example of a specific configuration will be described with reference to the cross-sectional view of FIG. FIG. 1 is a partial sectional view showing the vicinity of the image carrier 20 shown in FIG. The conductive brush roller of the charging unit 22 is supported so as to rotate in contact with each image carrier 20 at a predetermined position, and an image writing unit 23 including an organic EL array exposure head is provided on the downstream side of the charging unit 22. Each image carrier 20 is positioned and supported in parallel therewith. A case 50 that covers the image writing means 23 is provided on the downstream side of the image writing means 23. The wall surface of the case 50 is provided with an opening 51 for contacting the developing roller 33 of the developing unit 24 corresponding to each image carrier 20.

  A shielding part 52 of the case 50 is left between each opening 51 and the image writing means 23, and a shielding part 53 of the case 50 is left between the charging means 22 and the image writing means 23. Yes. The shielding portions 52, 53, particularly the shielding portion 52 between the opening 51 and the image writing means 23, prevent ultraviolet rays from reaching the light emitting portion made of the organic EL material in the image writing means 23 from the outside.

  At one end of the shielding portion 52, a flange portion 52a extending in the direction of the rod lens array 65 is provided. Further, a flange portion 53 a extending in the direction of the rod lens array 65 is also provided at one end of the shielding portion 53. A shielding plate 84 is provided between the flange portion 52a and the flange portion 53a. A light guide slit 84 x is formed in the shielding plate 84. The size of the light guide slit 84x is formed so that only the output light of the light emitting unit 63 is projected onto the image plane. That is, the output light from the light emitting unit 63 passes through each rod lens 81 of the rod lens array 65 and is projected onto the image carrier. The stray light is shielded by the shielding plate 84 and is not projected onto the image carrier. Instead of providing the shielding plate 84, a cover integrated with the shielding portions 52 and 53 may be provided, and the light guide slit 84x may be formed in the cover.

  By providing such shielding means as stray light projection preventing means, the stray light reflected by the cathode second layer 79b having a high reflectivity such as Al can be shielded. Therefore, it is possible to prevent ghost spots from being formed on the image carrier due to stray light. That is, it is possible to prevent image unevenness and improve the print quality.

  FIG. 2 is an explanatory view showing another embodiment of the present invention. Portions corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted. In the example of FIG. 2, the periphery of the rod lens array 65 is covered with a light guide cover 86. The light guide cover 86 has a substantially truncated cone shape, and has an opening 86a at the tip. From the opening 86a, output light from the light emitting unit 63 that has passed through each rod lens of the rod lens array 65 is projected onto the image carrier. By providing such a light guide cover 86, it is possible to prevent ghost spots from being formed on the image carrier by stray light.

  FIG. 3 is an explanatory diagram showing the light guide cover 86 described in FIG. 2 in an enlarged manner. A light emitting unit 63 is formed on one surface of the glass substrate 62, and a support base 85 is provided on the image carrier side of the glass substrate 62. A rod lens array 65 is attached to the support base 85. A light guide cover 86 having a substantially truncated cone shape is provided around the rod lens array 65. The output light L of the light emitting unit 63 is projected from the opening 86a formed at the tip of the light guide cover 86 onto the image carrier.

  The action of the light guide cover 86 can prevent the formation of a ghost spot on the image carrier due to stray light as described above, and can also be used as an alignment member between the exposure position of the image carrier and the rod lens. . For this reason, it is possible to prevent displacement of the rod lens. In addition, the scattered toner can be prevented from adhering to the rod lens, and contamination of the rod lens can be prevented.

  In the tandem type image forming apparatus using the optical head according to the embodiment of the present invention, it is possible to prevent the deterioration of the print quality due to the formation of the ghost spot. Further, this image forming apparatus includes an intermediate transfer member, and in the image forming apparatus including the intermediate transfer member, it is possible to prevent deterioration in print quality due to formation of a ghost spot.

  The optical head of the present invention and the image forming apparatus using the optical head have been described based on the embodiments. However, the present invention is not limited to these embodiments, and various modifications can be made.

It is sectional drawing which shows embodiment of this invention. It is sectional drawing which shows embodiment of this invention. It is sectional drawing which shows embodiment of this invention. 1 is a longitudinal side view of an image forming apparatus according to the present invention. It is a perspective view of an optical head. It is sectional drawing which shows embodiment of this invention. It is sectional drawing of the light emission part vicinity in the optical head of this invention. It is sectional drawing of the subscanning direction of an optical head. It is explanatory drawing which shows the example of a ghost spot.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Housing main body, 6 ... Image forming unit, 9 ... Transfer belt unit, 10 ... Paper feed unit, 11 ... Secondary transfer unit, 12 ... Fixing unit, 13 ... Recording medium conveyance means, 16 ... Intermediate transfer belt, 19 ... secondary transfer roller, 20 ... image carrier, 21 ... primary transfer member, 22 ... charging means, 23 ... image writing means (optical head), 24 ... developing means, 25 ... image carrier unit (Image carrier cartridge), 33... Developing roller, 50 .. case, 51... Opening, 52, 53... Shielding portion, 60 .. housing, 61 ... organic EL light emitting element array, 62. ... cover glass, 65 ... gradient index rod lens array, 66 ... cover, 71 ... TFT (thin film transistor), 79a ... first cathode layer, 79b ... second cathode layer, 81 ... Lens, 84 ... shield plate, 84x ... guiding slit, 86 ... guide cover, P ... recording medium

Claims (7)

In an optical head that includes a light-transmitting substrate, an organic EL light-emitting element formed on the substrate, and a lens array optical system, and forms an image on an image carrier by the lens array optical system, stray light is the image An optical head provided with shielding means for preventing projection onto a carrier. The said shielding means is a cover which covers the said image carrier in which the light guide slit which projects only the output light of the said organic EL light emitting element on an image surface is formed, The said support | carrier is characterized by the above-mentioned. Optical head. The stray light shielding means is a light guide cover that covers the lens array optical system and is provided with an opening for projecting output light of the organic EL light emitting element onto an image plane. The optical head described in 1. The optical head according to claim 3, wherein the light guide cover has a substantially truncated cone shape. The optical head according to claim 1, wherein the substrate is a glass substrate. At least two image forming stations in which image forming units including a charging unit, a line head according to any one of claims 1 to 5, a developing unit, and a transfer unit are arranged around an image carrier. An image forming apparatus provided as described above, wherein a transfer medium passes through each station and forms an image by a tandem method. The image forming apparatus according to claim 6, further comprising an intermediate transfer member.

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