Abstract:
An optical head is adapted to form an electrostatic latent image on an image carrier. A transparent substrate has a first face adapted to oppose the image carrier and a second face opposing the first face. An organic EL photo emitter is disposed so as to oppose the second face of the substrate. In the photo emitter, a light emitting layer is adapted to emit light irradiating the image carrier to form the electrostatic latent image. An electrode layer is laminated on the light emitting layer. A reflection reducer eliminates stray light generated when the light emitted from the light emitting layer is reflected by at least the electrode layer.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to an optical head and an image forming apparatus incorporating the same.  
         [0002]     Generally, a toner image forming device of an electrophotographic system comprises: a photosensitive body as an image carrier having a photosensitive layer on an outer peripheral surface thereof; a charger that uniformly charges the outer peripheral surface of the photosensitive body with electricity; an exposer for selectively exposing the outer peripheral surface, which is uniformly charged with electricity by the charger, to form an electrostatic latent image; and a developing device that applies toner serving as a developer to the electrostatic latent image formed by the exposer to make the latent image a visible image (toner image).  
         [0003]     An image forming apparatus of a tandem type that forms a color image includes one of an intermediate transfer belt type, in which the toner image forming device described above are arranged in plural (for example, four) for an intermediate transfer belt, toner images formed on the photosensitive body by the single color toner image forming device are sequentially transferred to the intermediate transfer belt, and toner images of plural colors (for example, yellow, cyan, magenta, black) are overlapped together on the intermediate transfer belt to obtain a full color image on the intermediate transfer belt.  
         [0004]     In the image forming apparatus of a tandem type, an optical head provided with a LED array or an organic EL element array is sometimes used as exposer. For example, Japanese Patent Publication No. 11-138899A discloses a light emitting diode array, in which light emitting diodes are mounted on a single chip.  
         [0005]     An explanation will be given to an example of an optical head, in which an organic EL element is used for a light source and an image is formed on an image carrier by a rod lens array optical system.  FIG. 6  shows such an optical head (image writer)  23  in a direction that the image carrier moves. A rod lens array  65  in which gradient index rod lenses  81  are arrayed is mounted to an opaque housing  60 . An photo emitter array  61  is mounted so as to face a back face of the rod lens array  65  in the housing  60 .  
         [0006]     An opaque cover  66  shields the photo emitter array  61  in the housing from a back face side of the housing  60 . The reference numeral  63  denotes a photo emitter (organic EL element), and  64  a cover glass. A plate spring  67  pushes the cover  66  against the back face of the housing  60  to close an interior of the housing  60  in a light-tight manner. The housing  60  covers a periphery of a glass substrate  62  but opens a side thereof facing an image carrier  20 . Thus light outgoing from the photo emitter  63  is projected onto the image carrier  20  through the rod lens  81 .  
         [0007]     In the optical head shown in  FIG. 6 , a ghost light spot  93  is sometimes formed on the image carrier  20 . The reason for this will be described below. When the photo emitter  63  is to be formed, an anode and a cathode are used. Since the cathode is formed from aluminum or the like, it serves as a mirror to reflect stray light in the grass substrate  62 . Therefore, reflected light  95  transmits through the rod lens  81  whereby the ghost light spot  93  is formed on the image carrier  20 .  
         [0008]      FIG. 7  shows the image carrier  20  by seeing through the rod lens array  65 . In this figure, the reference numerals  91 ,  92  denote exposure spots formed on the image carrier  20  by the photo emitter  63 , CL denotes a center line of rod lens array  65 , and  93 ,  94  denote ghost light spots. The ghost light spots include a large ghost light spot  93  formed to be concentric with the respective rod lenses  81 , and a small ghost light spot  94  formed in the vicinity of the border between adjacent rod lenses  81 . Such ghost light spots  93 ,  94  are formed on the image carrier  20  whereby there is caused a problem that image unevenness is formed to deteriorate the quality of image formation.  
       SUMMARY OF THE INVENTION  
       [0009]     It is therefore an object of the invention to provide an optical head that eliminates formation of any ghost light spot on an image carrier due to stray light, and to provide an image forming apparatus incorporating such an optical head.  
         [0010]     In order to achieve the above object, according to the invention, there is provided an optical head, adapted to form an electrostatic latent image on an image carrier, comprising:  
         [0011]     a transparent substrate, having a first face adapted to oppose the image carrier and a second face opposing the first face;  
         [0012]     an organic EL photo emitter, disposed so as to oppose the second face of the substrate and comprising: 
        a light emitting layer, adapted to emit light irradiating the image carrier to form the electrostatic latent image; and     an electrode layer, laminated on the light emitting layer; and        
 
         [0015]     a reflection reducer, eliminating stray light generated when the light emitted from the light emitting layer is reflected by at least the electrode layer.  
         [0016]     With this configuration, since any ghost light spot is not formed on the image carrier due to the stray light, it is possible to prevent generation of image unevenness. Accordingly, it is possible to improve the image formation quality.  
         [0017]     The reflection reducer may include an anti-reflection film disposed on a surface of the electrode layer facing the light emitting layer.  
         [0018]     The reflection reducer may include an anti-reflection coating provided on a surface of the electrode layer facing the light emitting layer.  
         [0019]     The reflection reducer may include a surface of the electrode layer facing the light emitting layer a surface roughness of which is made greater than a surface roughness of any other part of the electrode layer.  
         [0020]     The reflection reducer may include a light absorbing layer provided on the first face of the substrate.  
         [0021]     The reflection reducer may include a light reflecting layer provided on the first face of the substrate, and a light absorbing layer provided on end faces of the substrate connecting the first face and the second face.  
         [0022]     The reflection reducer may include a light reflecting layer provided on the first face of the substrate, and a light leading member provided on end faces of the substrate connecting the first face and the second face, and adapted to lead light reflected by the light reflecting layer toward an area on the image carrier to be irradiated with the light emitted from the photo emitter.  
         [0023]     The reflection reducer may include an anti-reflection film disposed on the second face of the substrate.  
         [0024]     The reflection reducer may include an anti-reflection coating provided on the second face of the substrate.  
         [0025]     The reflection reducer may include the second face of the substrate a surface roughness of which is made greater than a surface roughness of the first face of the substrate.  
         [0026]     The reflection reducer may include a cover member adapted to be disposed between the first face of the substrate and the image carrier. In this case, the cover member is formed with an aperture adapted to allow only the light emitted from the photo emitter to pass therethrough.  
         [0027]     Here, the cover member may be shaped into a frustum, and the aperture is formed at an apex portion thereof.  
         [0028]     The substrate may be comprised of glass.  
         [0029]     According to the invention, there is also provided an image forming apparatus, comprising:  
         [0030]     an image carrier; and  
         [0031]     an optical head, operable to form an electrostatic latent image on the image carrier, and comprising: 
        a transparent substrate, having a first face opposing the image carrier and a second face opposing the first face;     an organic EL photo emitter, disposed so as to oppose the second face of the substrate and comprising: 
            a light emitting layer, operable to emit light irradiating the image carrier to form the electrostatic latent image; and     an electrode layer, laminated on the light emitting layer; and    
               
 
         [0036]     a reflection reducer, eliminating stray light generated when the light emitted from the light emitting layer is reflected by at least the electrode layer 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]     The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:  
         [0038]      FIG. 1  is a schematic section view of a photo emitter in an optical head according to a first embodiment of the invention;  
         [0039]      FIG. 2  is a section view of an image forming apparatus incorporating the optical head;  
         [0040]      FIG. 3  is an enlarged section view of a part of an image forming unit in the image forming apparatus;  
         [0041]      FIG. 4  is a perspective view of the optical head;  
         [0042]      FIG. 5  is a section view of the optical head;  
         [0043]      FIG. 6  is a section view of a related-art optical head;  
         [0044]      FIG. 7  is a diagram showing a positional relationship between rod lenses in the related-art optical head and light spots formed by the related-art optical head;  
         [0045]      FIG. 8  is a schematic section view of a photo emitter in an optical head according to a second embodiment of the invention;  
         [0046]      FIG. 9  is a schematic section view of a photo emitter in an optical head according to a third embodiment of the invention;  
         [0047]      FIG. 10  is a schematic section view of a photo emitter in an optical head according to a fourth embodiment of the invention;  
         [0048]      FIG. 11  is a schematic section view of a photo emitter in an optical head according to a fifth embodiment of the invention;  
         [0049]      FIG. 12  is a section view of a part of an image forming unit including an optical head according to a sixth embodiment of the invention;  
         [0050]      FIG. 13  is a section view of a part of an image forming unit including an optical head according to a seventh embodiment of the invention; and  
         [0051]      FIG. 14  is a side view of a part of the optical head of  FIG. 13 . 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0052]     Embodiments of the invention will be described with reference to the accompanying drawings.  
         [0053]      FIG. 2  shows an image forming apparatus  1  according to a first embodiment of the invention, which is a type that an intermediate transfer belt is incorporated.  
         [0054]     The image forming apparatus  1  comprises: a housing body  2 ; a first door cover  3  mounted to a front face of the housing body  2 ; and a second door cover (serving as an ejection tray)  4  mounted to an upper face of the housing body  2 . The first door cover  3  comprises a lid  3 ′ which is able to opened and closed in association with the first door cover  3  or independently.  
         [0055]     Arranged in the housing body  2  are an electrical equipment box  5  that houses therein a power circuit board and a control circuit board, an image forming unit  6 , a ventilation fan  7 , a transfer belt unit  9 , and a sheet feeding unit  10 . Arranged in the first door cover  3  are a secondary transfer unit  11 , a fuser unit  12 , and a sheet transporter  13 . Expendable items in the image forming unit  6  and the sheet feeding unit  10  are made detachable from the body, in which case the items together with the transfer belt unit  9  can be removed for repair or exchange.  
         [0056]     The transfer belt unit  9  comprises a drive roller  14  rotated by a drive source (not shown) arranged below the housing body  2 , a follower roller  15  arranged obliquely upwardly of the drive roller  14 , an intermediate transfer belt  16  stretched between the two rollers  14 ,  15  to be circulated in a direction indicated by an arrow as shown, and a cleaner  17  retractably coming in contact with a surface of the intermediate transfer belt  16 . In this embodiment, the follower roller  15  and the intermediate transfer belt  16  are arranged in a direction, in which they are inclined relative to the drive roller  14  leftward in the figure.  
         [0057]     A primary transfer member  21  composed of a leaf spring electrode in opposition to the image carriers  20  of respective image forming stations Y, M, C, K described later is caused by its elastic force to abut against a back face of the intermediate transfer belt  16 , and transfer bias is applied to the primary transfer member  21 . A test pattern sensor  18  is mounted on a support frame  9   a  of the transfer belt unit  9  to be close to the drive roller  14 . The test pattern sensor  18  is one, which serves to position respective color toner images on the intermediate transfer belt  16  and to detect densities of respective color toner images to correct color misalignment and image densities of respective color images.  
         [0058]     The image forming unit  6  comprises a plurality (four in the embodiment) of image forming stations Y (for yellow), M (for magenta), C (for cyan), K (for black), by which images of different colors are formed, and the image forming stations Y, M, C, K, respectively, comprise an image carrier  20  composed of a photosensitive drum, a charger  22 , an optical head (image writer)  23 , and a developing device  24 , which are arranged around the image carrier  20 . The charger  22 , the image writer  23 , and the developing device  24  are denoted by reference numerals only for the image forming station Y, and reference numerals are omitted for other image forming stations since the stations are the same in construction That order, in which the respective image forming stations Y, M, C, K are arranged, may be changed arbitrarily.  
         [0059]     The image carriers  20  of the respective image forming stations Y, M, C, K are arranged to abut against a surface of the intermediate transfer belt  16 , facing downward. Consequently, the respective image forming stations Y M, C, K are also arranged to be inclined leftward relative to the drive roller  14  in the figure. The image carriers  20  are rotated as indicated by an arrow in the figure in the circulating direction of the intermediate transfer belt  16 . The intermediate transfer belt  16  is provided with the cleaner  17 , which recovers toner left on the intermediate transfer belt after the transfer is performed.  
         [0060]     The charger  22  is composed of a conductive brush roller connected to a high-voltage generating source, and an outer periphery of the brush abuts against and rotates at two to three times a circumferential speed of the image carrier  20  in a reverse direction to the rotating direction of the image carrier  20  to uniformly charge a surface of the image carrier  20  with electricity. Since the use of such charger  22  makes it possible to charge a surface of the image carrier with a very small electric current, contamination inside and outside the apparatus by a large amount of ozone as in the corona electrical charging system is eliminated. Also, since the brush roller abuts softly against the image carrier  20 , toner left thereon after the transfer is performed is hard to adhere to the charging roller, so that it is possible to ensure a stable image quality and reliability in the apparatus.  
         [0061]     The image writer  23  is an optical head in which organic EL elements are arrayed in an axial direction of the image carrier  20 . Since an optical path length in such an optical head can be made shorter than a laser scanning optical system, the optical head can be made compact. Thus, it can be arranged close to the image carrier  20  and make the whole apparatus small in size. In this embodiment, the image carrier  20 , the charger  22 , and the image writer  23  in the respective image forming stations Y, M, C, K are integrated as one image carrier unit  25 , and mounted on the support frame  9   a  together with the transfer belt unit  9  to be made capable of exchange, whereby positioning of the optical head relative to the image carrier  20  is preserved. It is configured such that the optical head is exchanged together with the image carrier unit  25 .  
         [0062]     Subsequently, the construction of the developing device  24  will be described with the image forming station K as a typical example. The developing device  24  comprises a toner container  26  that stores toner (shown by hatched portions in the figure), a toner storing part  27  formed in the toner container  26 , a toner agitating member  29  arranged in the toner storing part  27 , a partition member  30  compartmented and formed in an upper region of the toner storing part  27 , a toner supplying roller  31  arranged above the partition member  30 , a blade  32  provided on the partition member  30  to abut against the toner supplying roller  31 , a developing roller  33  arranged so as to abut against the toner supplying roller  31  and the image carrier  20 , and a control blade  34  that abuts against the developing roller  33 . The image carrier  20  is rotated in the circulating direction of the intermediate transfer belt  16 , and the developing roller  33  and the toner supplying roller  31  are rotated as indicated by an arrow in the figure in a reverse direction to the rotating direction of the image carrier  20 .  
         [0063]     The sheet feeding unit  10  comprises a sheet feeding part composed of a sheet feeding cassette  35 , in which recording media P are stacked and held, and a pickup roller  36  that feeds the recording media P one by one from the sheet feeding cassette  35 . Provided in the first door cover  3  are a resist roller pair  37  that regulates timing, in which the recording media P are fed to the secondary transfer part, the secondary transfer unit  11  brought into pressure contact with the drive roller  14  and the intermediate transfer belt  16 , the fuser unit  12 , the sheet transporter  13 , a sheet ejecting roller pair  39 , and a transporting path  40  for double-sided printing.  
         [0064]     The fuser unit  12  comprises a heating roller  45  that houses therein a heating element such as a halogen heater, etc., a pressure roller  46  that pushes and biases the heating roller  45 , a belt stretcher  47  arranged pivotably relative to the pressure roller  46 , and a heat resisting belt  49  stretched between the heating roller  45  and the belt stretching member  47 , and a color image secondarily transferred to a recording medium is fused therewith at a predetermined temperature in a nipping portion formed by the heating roller  45  and the heat resisting belt  49 . In the embodiment, it becomes possible to arrange the fuser unit  12  in a space formed obliquely upwardly of the intermediate transfer belt  16 , in other words, a space on an opposite side of the image forming unit  6  to the intermediate transfer belt  16 , so that it is possible to decrease heat transfer to the image forming unit  6  and the intermediate transfer belt  16 .  
         [0065]     As shown in  FIG. 3 , the brush roller of the charger  22  is rotatably supported while being abutted against a predetermined position of the image carrier  20 . The image writer  23  is disposed in a downstream side of the charger  22  relative to the rotating direction of the image carrier  20 . An opening  51  is formed on a casing  50  in the downstream side of the image writer  23  to permit the developing roller  33  of the developing device  24  to abut against the image carrier  20  therethrough.  
         [0066]     A shielding portion  52  of the casing  50  is left between each of the openings  51  and the image writer  23 , and a shielding portion  53  of the casing  50  is left between the charger  22  and the image writer  23 . The shielding portions  52 ,  53 , in particular, the shielding portion  52  between the opening  51  and the image writer  23  prevents ultraviolet rays from reaching the photo emitter  63  in the image writer  23 . The reference numeral  82  denotes a cleaning pad that performs wiping in the case where the rod lens array  65  becomes dirty.  
         [0067]      FIG. 4  shows an example of a mechanism that correctly positions the image writer  23  relative to the image carrier  20  (a photosensitive drum) mounted to the image carrier unit  25 . The image carrier  20  shown in  FIG. 2  is mounted by a shaft thereof rotatably to the casing  50  of the image carrier unit  25 . Also, the photo emitter array  61  is held in the elongated housing  60 .  
         [0068]     The respective image writer  23  is fixed in a predetermined position by fitting positioning pins  69 , which are provided on both ends of the elongated housing  60 , in opposite positioning holes on the casing  50  and screwing and fixing lock screws into threaded holes of the casing  60  through screw insertion holes  68  provided on the both ends of the elongated housing  60 .  
         [0069]     As shown in  FIG. 5 , light emitted from the photo emitter  63  of the photo emitter array  61  transmits the glass substrate  62  to outgo toward the image carrier  20 . With the glass substrate  62 , a surface formed with the photo emitter  63  and that surface, from which light outgoes, are made substantially in parallel to each other.  
         [0070]     As shown in  FIG. 1 , the photo emitter array  61  comprises TFTs (thin film transistors)  71  made of polysilicon having a thickness of 50 nm and provided on the glass substrate  62 , which has a thickness of, for example, 0.5 mm, to control light emission of the respective photo emitters  63 . As shown in  FIG. 4 , the TFTs  71  are arranged so as not to intercept light La emitted from each of the photo emitters  63  which are arranged in a zigzag manner so as to form two rows.  
         [0071]     An insulating film  72  formed from SiO 2  having a thickness in the order of 100 nm is deposited on the glass substrate  62  except contact holes on the TFTs  71 , and anodes  73  formed from ITO having a thickness of 150 nm are formed so as to be connected to the TFTs  71  through the contact holes. Subsequently, an insulating film  74  formed from SiO 2  having a thickness in the order of 120 nm is deposited on regions corresponding to other positions than the photo emitters  63 .  
         [0072]     Banks  75  formed from polyimide having a thickness of 2 μm and formed with holes  76 , which correspond to the photo emitters  63 , are provided on the insulating film  74 , and an electron-hole injected layer  77  having a thickness of 50 nm and a light emitting layer  78  having a thickness of 50 nm are deposited, in this order from the anodes  73 , in the holes  76  of the banks  75 . A first cathode layer  79   a  formed from calcium having a thickness of 100 nm and a second cathode layer  79   b  formed from aluminum having a thickness of 200 nm are deposited in this order in a manner to cover an upper face of the light emitting layer  78 , inner surfaces of the holes  76 , and outer surfaces of the banks  75 .  
         [0073]     The photo emitter  63  of the photo emitter array  61  is provided above the layers to be covered by the cover glass  64  having a thickness in the order of 1 mm and inert gas  80  such as nitrogen gas is filled therebetween. Light emission from the photo emitters  63  is performed on a side of the glass substrate  62 . Outgoing light La, Lb from the light emitting layer  78  is projected onto the image carrier  20  through the rod lenses  81 . Since it is configured that the photo emitters (organic EL elements)  63  are formed on the glass substrate  62 , light transmission is made favorable. In addition, the photo emitters  63  can be easily fabricated with an arbitrary shape.  
         [0074]     When the photo emitters  63  operate to emit light, stray light is formed due to various factors in addition to the normal outgoing light La, Lb outgoing toward the image carrier  20 . As described above, the second cathode layer  79   b  is formed from metal, such as aluminum, having a high reflection coefficient. Therefore, a part of stray light is reflected by the second cathode layer  79   b  to transmit the glass substrate  62  to form ghost light spots on the image carrier through the rod lenses  81 .  
         [0075]     In this embodiment, the optical head is constructed so that such ghost light spots are not formed on the image carrier. As an example of a concrete construction, measures are taken to decrease the cathode layers in reflection coefficient. Specifically, an anti-reflection layer  89  is formed on a surface of the first cathode layer  79   a  facing the light emitting layer  78  by sticking of an anti-reflection film, for example. With this configuration, the stray light is reflected by the second cathode layer  79   b  having a high reflection coefficient can be reduced, thus preventing that deterioration in image formation quality, which is caused by formation of ghost light spots on the image carrier  20 .  
         [0076]     The anti-reflection film is fabricated by alternately laminating a metal, a dielectric substance, and a transparent conductive material on a film by sputtering or deposition. Since such an anti-reflection film has used for various applications, it is possible to fabricate it with low cost.  
         [0077]     Alternatively, the anti-reflection layer  89  may be formed by coating an anti-reflection coating liquid on the surface of the cathode layer facing the light is emitting layer  78 . The anti-reflection coating liquid is coated in the wet process. In this case, reflection of stray light can be prevented by a simple processing. In addition, instead of providing the anti-reflection layer  89 , the cathode layer can be decreased in reflection coefficient for stray light by increasing surface roughness of the surface of the second cathode layer  79   b  facing the light emitting layer  78 . In this case, since any further member is not provided, cost reduction can be attained.  
         [0078]     Next, a second embodiment of the invention will be described. Components similar to those in the first embodiment will be designated by the same reference numerals and repetitive explanations for those will be omitted.  
         [0079]     In this embodiment, as shown in  FIG. 8 , a cover layer  85  is formed on a surface of the glass substrate  62  facing the image carrier  20 . The cover layer  85  is provided as a light absorbing member coated with, for example, a black paint.  
         [0080]     The cover layer  85  is formed outside an effective light projecting region which is defined between dashed chain lines La and Lb in  FIG. 8  Therefore, the cover layer  85  does not make an obstacle to projection of light emitted from the photo emitters  63  onto an image forming region of the image carrier  20 , a decrease in efficiency of projection is not incurred. By providing the cover layer  85 , it is possible to absorb stray light Lx, Ly reflected by the second cathode layer  79   b . Accordingly, it is possible to prevent ghost light spots from being formed on the image carrier  20  by stray light Lx, Ly. Since the light absorbing member can be formed by coating of a black paint, the construction can be made inexpensive.  
         [0081]     Next, a third embodiment of the invention will be described. Components similar to those in the second embodiment will be designated by the same reference numerals and repetitive explanations for those will be omitted.  
         [0082]     In this embodiment, as shown in  FIG. 9 , a cover layer  86  is formed by a reflection mirror, that is, a light reflecting member. The cover layer  86  is also formed outside the effective light projecting region with respect to the image carrier  20  as well as the second embodiment. Further, light absorbing members  87  are provided on ends of the glass substrate  82 . The light absorbing members  87  can be structured to be coated with a black paint.  
         [0083]     With the above configuration, stray light Lx and Ly reflected by the cover layer  86  to propagate in the glass substrate  62  to reach the ends thereof. Here, the light is absorbed by the light absorbing members  87  to be prevented from being projected onto the image forming region of the image carrier  20 .  
         [0084]     Next, a fourth embodiment of the invention will be described. Components similar to those in the third embodiment will be designated by the same reference numerals and repetitive explanations for those will be omitted.  
         [0085]     In this embodiment, as shown in  FIG. 10 , light leading members  88  are provided on ends of the glass substrate  62  so that stray light Lx propagating in the glass substrate  62  to reach the ends thereof is made incident upon the light leading members  88 . Stray light Lx is irradiated outside the image forming region from the light leading members  88 . Likewise, stray light Ly transmits the light leading members  88  formed on the ends of the glass substrate  62  to be irradiated outside the image forming region.  
         [0086]     Next, a fifth embodiment of the invention will be described. Components similar to those in the second embodiment will be designated by the same reference numerals and repetitive explanations for those will be omitted.  
         [0087]     In this embodiment, as shown in  FIG. 11 , an anti-reflection layer  89  is formed on a surface of the glass substrate  62  facing the light emitters  63  in addition to the cover layer  85  as described in the second embodiment. The anti-reflection layer  89  is formed by sticking of an anti-reflection film. Stray light Lx having not been absorbed by the cover layer  85  propagates in the glass substrate  62  as indicated by dashed lines, but the stray light Lx is prevented from being again reflected to propagate in the glass substrate  62  by the anti-reflection layer  89 . Lw denotes stray light produced by a photo emitter adjacent to the photo emitter  63 .  
         [0088]     The formation of the anti-reflection layer  89  may be applicable with respect to the configurations of the third and fourth embodiments. By providing a plurality of measures for preventing stray light from being projected onto the image carrier  20 , it is possible to effectively improve the image formation quality.  
         [0089]     Next, a sixth embodiment of the invention will be described. Components similar to those in the first embodiment will be designated by the same reference numerals and repetitive explanations for those will be omitted.  
         [0090]     In this embodiment, as shown in  FIG. 12 , a flange  52   a  is provided on one end of the shielding portion  52  to extend toward the rod lens array  65 . Also, a flange  53   a  is provided on one end of the shielding portion  53  to extend toward the rod lens array  65 . A shielding plate  84  is provided between the flange  52   a  and the flange  53   a . The shielding plate  84  is formed with a light leading slit  84   x . The light leading slit  84   x  is formed to be sized so as to permit only light emitted from the photo emitter  63  to be projected onto the image carrier  20 . That is, light emitted from the photo emitter  63  transmits the respective rod lenses  81  of the rod lens array  65  to be projected onto the image carrier  20 . Stray light is shielded by the shielding plate  84  not to be projected onto the image carrier  20 . In addition, instead of providing the shielding plate  84 , a cover made integral with the shielding portions  52 ,  53  may be provided and the light leading slit  84   x  may be formed on the cover.  
         [0091]     With this configuration, it is possible to shield stray light reflected by the second cathode layer  79   b . Accordingly, it is possible to prevent ghost light spots from being formed on the image carrier  20  by the stray light. That is, it is possible to prevent generation of image unevenness to improve the image formation quality.  
         [0092]     Next, a seventh embodiment of the invention will be described. Components similar to those in the sixth embodiment will be designated by the same reference numerals and repetitive explanations for those will be omitted.  
         [0093]     In this embodiment, as shown in  FIG. 13 , a light leading cover  86  covers a periphery of a rod lens array  65 . The light leading cover  86  is in the form of a substantially frustum to be formed at an apex portion thereof with an opening  86   a . Light emitted from photo emitters  63  to transmit the respective rod lenses  81  of the rod lens array  65  is projected onto the image carrier  20  from the opening  86   a . With this configuration, it is possible to prevent ghost light spots from being formed on the image carrier  20  by the stray light.  
         [0094]     As shown in  FIG. 14 , the photo emitters  63  are formed on one surface of the glass substrate  62 , and a support base  85  is provided on another surface of the glass substrate  62  facing the image carrier  20 . The rod lens array  65  is mounted on the support base  85 .  
         [0095]     The light leading cover  86  serves to prevent ghost light spots from being formed on the image carrier  20  by stray light, and can be used as a member for positioning the rod lens array  65  relative to the image carrier  20 . Therefore, it is possible to prevent positional deviation of the rod lenses  81 . Also, it is possible to prevent scattered toner from adhering to the rod lenses  81  to achieve prevention of contamination of the rod lenses  81 .  
         [0096]     Although the present invention has been shown and described with reference to specific preferred embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.