JP2005266533A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus where toner is surely prevented from intruding into an exposure unit in the case of writing image information on a photoreceptor drum by exposure, and the image information is accurately written on the photoreceptor drum by the exposure by surely preventing soiling by the toner on the optical path of exposing light, and also which is made compact in a horizontal direction. <P>SOLUTION: The image forming apparatus where the exposure unit for writing an electrostatic latent image on the photoreceptor drum 3 by the exposure is arranged below a developing tank 21 in which the toner is stored is provided with an aperture part 1b on the upper surface of an exposure unit case 1a positioned on the optical path Z of light from the exposure unit so as not to become the hindrance of the optical path of the light, and a glass plate G at the aperture part so as to erect nearly perpendicularly to a horizontal line. The glass material is composed of dense flint glass whose refractive index is ≥1.7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a printer that prevents contamination of an exposure unit due to natural falling of the developer or scattering of the developer, and in particular, on an optical path of light exposed from the exposure unit. It relates to measures to prevent contamination and to make the exposure unit compact.

  2. Description of the Related Art Conventionally, a paper feeding unit, a printing unit, a paper discharging unit, and an optical unit (document reading optical unit for printing and image information that has been read are written on an electrostatic latent image carrier. The arrangement of the exposure optical unit is determined in consideration of the compactness of the apparatus, the ease of operation, the ease of designing the apparatus, and the like.

  Usually, the developing tank for storing the developer is disposed on the side surface of the photoreceptor, and the exposure optical unit (in recent years, write heads such as LSU, EL, and LED are used) are disposed above or obliquely above the photoreceptor. Various forms of exposure are used.

  On the other hand, a color image forming apparatus pursuing compactness of the apparatus requires a photoreceptor and a developing tank corresponding to each hue, but the fixing device and the paper transport path are useless, so that the color can be obtained with one paper pass. In order to obtain an image, a color image forming apparatus called a “tandem method” is being developed. There are two methods in this tandem method, one is a method for directly transferring image information to be visualized on the photoconductor of each hue onto the paper, and the other is to be visualized on the photoconductor of each hue. There are two types of techniques in which image information is temporarily laminated on an intermediate medium (intermediate transfer member) and then transferred to a sheet in a single transfer process. In this case, the color image forming apparatus is provided with a photosensitive member for color such as yellow, magenta, and cyan and a developing tank, respectively. Of course, is also arranged.

  At this time, in the method using the intermediate transfer medium (hereinafter referred to as an endless belt) as in the latter case, the arrangement position of the photoconductor arranged around the endless belt determines the printing speed (first copy speed) of the apparatus. It will contribute. In other words, color photoreceptors such as yellow, magenta, and cyan and developing tanks are arranged in order from the part far from the transfer unit that collectively transfers to the paper, and the black photoreceptor and developer tank that prints in the closest part are arranged. Arrangement is an essential condition for improving the printing speed.

  On the other hand, in recent years, many built-up type devices called a front access method have been developed to reduce the area occupied by the image forming apparatus. That is, a printing paper storage / feed unit is arranged at the bottom of the apparatus, a printing unit is arranged at the top thereof, and a scanner unit for reading image information of a document is arranged at the top of the apparatus. Many devices have been put on the market in which discharging is performed on the side of the device or on the upper part of the printing unit and on the lower side of the scanner unit.

  Considering the case of applying a technique using an endless belt in a tandem system in such an apparatus, the paper transport direction is basically transported from the bottom to the top, and the transfer unit is rotated in the forward direction in the paper transport direction. In consideration of the above-described optimal arrangement position of the sheet transfer unit, the photosensitive member and developing tank of each hue, and the improvement of the printing speed, the arrangement from the bottom of the apparatus is directed to the sheet storage / feed unit and the photosensitive member. The exposure optical unit, the photoreceptor and the developing tank, and the endless belt are arranged.

  As described above, when the developing tank is disposed on the exposure optical unit and the developing region (usually referred to as a developing nip) formed by the photosensitive member and the developing sleeve is disposed, the developer staying in the developing nip portion is Due to the flow of wind generated from the peripheral speed of the photosensitive member and the developing sleeve and the loss of the electric field action due to the relationship with the electric field of the developing sleeve, it may fall naturally due to gravity or be scattered in the machine. .

  As a result, the developer is contaminated in the exposure optical unit disposed in the lower part of the developing tank, the written image is disturbed, the polygon mirror that rotates at high speed is damaged, or the fθ lens and the plurality of mirrors are stained. The print quality will be reduced.

  From this point of view, it is necessary to have a structure that shields the exterior part from the outside in order to keep the exposure optical part clean at all times, because the exposure optical part is disposed below the photoreceptor and the developing tank. .

  However, since it is impossible to block the optical path from the exposure optical unit when writing image information on the photoconductor, it is necessary to make the part that hits the optical path as an opening. In this case, the developer is exposed from the opening. It will enter into the optical part.

  Therefore, a shutter that can be opened and closed is used for the portion (opening) that hits the optical path from the exposure optical unit, so that contamination due to the intrusion of the developer from the opening is prevented and the exposure optical unit is always kept clean. Have been proposed (see, for example, Patent Document 1).

As another method, there is a method in which glass is disposed in a portion corresponding to the optical path of the exposure unit to prevent contamination due to the intrusion of the developer from the opening portion and to keep the exposure optical portion clean.
Japanese Patent Laid-Open No. 04-323669

  However, if the shutter that can be opened and closed is used for the portion (opening) that hits the optical path from the exposure unit such as the exposure optical unit as described above, can the shutter mechanism normally satisfy the function for the operation of the apparatus? There is anxiety about whether or not. That is, most of the developer falls and scatters during the printing process. At that time, the exposure unit is also in exposure to write image information on an image carrier such as a photoconductor, and the shutter. Must be open. Therefore, when the shutter is in the open state, the developer that falls or scatters cannot be blocked, and contamination by the developer in the exposure unit cannot be prevented, and the shutter function is fully utilized. That's not true. In short, this shutter prevents the developer from dropping when the apparatus is moved or when the developer or the image carrier is replaced, and when the image information is written on the image carrier by exposure. Contamination due to the intrusion of the developer into the exposure unit cannot be prevented.

  On the other hand, in the case where the glass is disposed in the portion (opening) that hits the optical path from the exposure unit as described above, the transparent glass is merely disposed on the optical path of the light to be exposed, even if the glass is cleaned. Even if the cleaning is performed regularly, there is a risk that the developer that falls or scatters will accumulate on the glass during the cleaning process until the next cleaning. The contaminated image information cannot be accurately written on the image carrier.

  Therefore, the developer is deposited on the optical path while preventing the contamination due to the intrusion of the developer into the exposure unit by standing the glass at a right angle to the horizontal line so that the developer that falls and scatters is difficult to accumulate. It is conceivable to prevent contamination due to the above.

  However, in the above-mentioned, since the optical path of the light that enters and exits the glass from the exposure unit is long in the substantially horizontal direction, the glass is used to irradiate the image carrier with the emitted light that is emitted from the glass. It is necessary to secure a horizontal distance between the image forming body and the image carrier, and the size of the image forming apparatus in the horizontal direction is inevitably increased.

  The present invention has been made in view of the above points, and the object of the present invention is to reliably prevent the developer from entering the exposure unit when writing image information on the image carrier by exposure, and Contamination due to the developer on the optical path of the light to be exposed can be reliably prevented, and image information can be accurately written on the image carrier by exposure, and the optical path design can be made more compact. An object of the present invention is to provide an image forming apparatus that can be realized.

  In order to achieve the above-mentioned object, the solution provided by the present invention is the above-mentioned image is provided below a developing tank containing a developer for developing an electrostatic latent image formed on an image carrier into a visible image. On the premise of an image forming apparatus in which an exposure unit for writing an electrostatic latent image on a carrier by exposure is disposed, the developer falls or scatters on the optical path of light exposed from the exposure unit toward the image carrier. A transparent member for preventing the exposure unit from being soiled is provided so as to be substantially perpendicular to the horizontal line. The transparent member is made of a material having a high refractive index.

  Due to this specific matter, the transparent member provided on the optical path of the light exposed from the exposure unit toward the image carrier, that is, the portion corresponding to the optical path from the exposure unit, is provided so as to stand substantially perpendicular to the horizontal line. Therefore, it is possible to reliably prevent contamination by the developer in the exposure unit by blocking the falling and scattering developer by the transparent member. Moreover, even if the developer that falls or scatters falls on the transparent member, the developer flows downward on the transparent member each time it falls, and the developer that falls or scatters does not accumulate on the transparent member. The contamination on the optical path by the developer is eliminated, and the image information can be accurately written on the image carrier by exposure. Furthermore, since the transparent member is made of a material having a high refractive index, there is a large angle difference between the incident angle and the exit angle of the optical path of light with respect to the transparent member. The optical path of the light emitted from the transparent member using the horizontal member is shortened in the horizontal direction, and the transparent member required for irradiating the optical path of the light emitted from the transparent member (emitted light) to the image carrier The distance in the horizontal direction from the image carrier becomes short, and the image forming apparatus can be made compact in the horizontal direction.

  Another solution is to place the electrostatic latent image on the image carrier below the developing tank containing a developer that develops the electrostatic latent image formed on the image carrier into a visible image. Similarly, assuming an image forming apparatus in which an exposure unit for writing an image by exposure is arranged, the exposure unit is contaminated by dropping or scattering of the developer on the optical path of light exposed from the exposure unit toward the image carrier. A transparent member is provided to prevent this. The transparent member is formed in a prism shape in which the side surface of the image carrier rises substantially perpendicular to the horizontal line and the side surface of the exposure unit is inclined.

  Because of this specific matter, a transparent member is provided on the optical path of light exposed from the exposure unit toward the image carrier, that is, the portion that hits the optical path from the exposure unit. It is possible to reliably prevent contamination by the developer in the exposure unit. In this case, the transparent member is formed in a prism shape in which the side surface of the image carrier rises substantially perpendicular to the horizontal line and the side surface of the exposure unit is inclined. Even if it falls on the side, the developer flows downward on the side of the image carrier of the transparent member every time it falls, and the developer that falls or scatters does not accumulate on the side of the image carrier of the transparent member. The contamination on the optical path by the developer is eliminated, and the image information can be accurately written on the image carrier by exposure. Furthermore, the prism-shaped transparent member can set a large angle difference between the incident angle and the exit angle of the light path of the light with respect to the transparent member, and the angle difference between the transparent members can be used for the light emitted from the transparent member. The optical path is shortened in the horizontal direction, and the distance in the horizontal direction between the transparent member and the image carrier required for irradiating the image carrier with the optical path of the light emitted from the transparent member (emitted light) is short. Thus, the image forming apparatus can be downsized in the horizontal direction.

  In particular, the following configurations are listed as specifying the image carrier side surface of the plate material.

  In other words, a surface coating layer is provided on the side surface of the image carrier (for example, a low-friction member, an antistatic agent) that has been subjected to a coating process that enhances the sliding property of the developer that has fallen onto the side surface of the transparent member. Agents).

  By this specific matter, when the developer that falls or scatters falls on the side of the image carrier of the transparent member, the developer actively flows downward on the transparent member by the surface coat layer, and the developer that falls or scatters is removed. Accumulation on the transparent member is effectively prevented, contamination on the optical path by the developer is more reliably eliminated, and image information can be written onto the image carrier more accurately by exposure.

  In short, in short, the transparent member that stands up substantially perpendicular to the horizontal line on the optical path of light exposed from the exposure unit toward the image carrier is made of a high refractive index material, or the side surface of the image carrier is a horizontal line. By forming a transparent member in the shape of a prism that stands upright and tilted on the side of the exposure unit, the developer that falls or scatters is blocked by the transparent member, ensuring contamination by the developer in the exposure unit. In addition, every time the developer that falls or scatters falls on the transparent member, it flows downward to prevent the developer from depositing on the transparent member, and the image information is exposed by eliminating contamination on the optical path by the developer. Thus, it is possible to accurately write on the image carrier. Furthermore, the optical path of the light can be shortened in a substantially horizontal direction by utilizing a large angle difference existing between the incident angle and the exit angle of the light path with respect to the transparent member, and the exposure unit can be made compact.

  Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, a case where the present invention is applied to a color printer will be described.

(Description of overall configuration of image forming apparatus)
FIG. 1 schematically shows the internal configuration of an image forming apparatus A according to this embodiment. The image forming apparatus A generates a multicolor (full color) image or a single color (monochrome) image on a predetermined sheet (recording paper) according to image data transmitted from the outside (for example, a terminal device such as a personal computer). To form. As illustrated, the image forming apparatus A includes an exposure unit 1, a developing device 2 (2a to 2d), a photosensitive drum 3 (3a to 3d) as an image carrier, and a charger 5 (5a to 5d). The cleaner unit 4 (4a to 4d), the intermediate transfer belt unit 8, the fixing device 12, the paper transport path S, the paper feed cassette 10, the paper discharge tray 15, and the like.

  The image data handled in the image forming apparatus A corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Accordingly, the developing device 2 (2a to 2d), the photosensitive drum 3 (3a to 3d), the charger 5 (5a to 5d), and the cleaner unit 4 (4a to 4d) generate four types of latent images corresponding to the respective colors. In FIG. 1, a is set to black, b is set to cyan, c is set to magenta, and d is set to yellow to form four image stations (image forming units). ing.

  The photosensitive drum 3 is arranged (attached) on the upper part of the image forming apparatus A, and an electrostatic latent image corresponding to image data is formed by irradiation of laser light from the exposure unit 1 as will be described later. Yes.

  The charger 5 is a charging means for uniformly charging the surface (photoconductor layer) of the photosensitive drum 3 to a predetermined potential. In addition to a contact type roller type or brush type charger, a charger type charging unit is also used. A vessel may be used.

  The exposure unit 1 is composed of a laser scanning unit (LSU) including a laser irradiation unit 1A and reflection mirrors 1B, 1B,... In an exposure unit case 1a. The laser irradiation unit 1A irradiates laser light for each hue based on the received image data. In addition, there is a method using, for example, an EL or LED writing head in which light emitting elements are arranged in an array. The exposure unit 1 exposes the charged photosensitive drum 3 according to the input image data, thereby forming an electrostatic latent image according to the image data on the surface of the photosensitive drum 3. have.

  The developing device 2 visualizes the electrostatic latent images formed on the respective photosensitive drums 3 with toners (developers) of respective colors (K, C, M, Y). These color toners are accommodated in the developing tanks 21a to 21d of the developing devices 2a to 2d for the respective image stations. And the said exposure unit 1 is arrange | positioned under each developing tank 21 (21a-21d).

  The cleaner unit 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  The intermediate transfer belt unit 8 disposed above the photosensitive drum 3 includes an intermediate transfer belt 7, an intermediate transfer belt drive roller 71, an intermediate transfer belt tension mechanism 73, an intermediate transfer belt driven roller 72, and a primary transfer roller. An intermediate transfer roller 6 (6a to 6d) and an intermediate transfer belt cleaning unit 9 are provided.

  The intermediate transfer belt drive roller 71, the intermediate transfer belt tension mechanism 73, the intermediate transfer roller 6, and the intermediate transfer belt driven roller 72 are stretched over the intermediate transfer belt 7, and the intermediate transfer belt 71 is rotated along with the rotation of the intermediate transfer belt drive roller 71. The belt 7 travels in the direction of arrow B.

  The intermediate transfer roller 6 is rotatably supported by a roller mounting portion in the intermediate transfer belt tension mechanism 73. As a result, the intermediate transfer rollers 6 a to 6 d are rotatably disposed on the inner surface side of the intermediate transfer belt 7 facing each photoconductor drum 3, and the toner image on the photoconductor drum 3 is also provided. Is transferred to the intermediate transfer belt 7.

  The intermediate transfer belt 7 is provided so as to be in contact with each photosensitive drum 3. Then, the toner images of the respective colors formed on the photosensitive drum 3 are sequentially superimposed and transferred onto the intermediate transfer belt 7, thereby forming a color toner image (multicolor toner composite image) on the intermediate transfer belt 7. It is like that. The intermediate transfer belt 7 is endlessly formed using a film having a thickness of about 100 μm to 150 μm.

  Transfer of the toner image from the photosensitive drum 3 to the intermediate transfer belt 7 is performed by the intermediate transfer roller 6 in contact with the back side (inner surface side) of the intermediate transfer belt 7. That is, a high voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charge polarity (−)) is applied to the intermediate transfer roller 6 in order to transfer the toner image. The intermediate transfer roller 6 is a roller whose base is a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm and whose surface is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). With this conductive elastic material, a high voltage can be uniformly applied to the intermediate transfer belt 7. In this embodiment, a roller electrode is used as the transfer electrode, but a brush or the like can also be used.

  As described above, the toner images visualized according to the hues on the photoreceptors 3a to 3d are stacked on the intermediate transfer belt 7 and become image information input to the apparatus. In this way, the laminated image information (composite image of multi-color toner) is transferred to a transfer roller that constitutes a transfer unit that is disposed at a contact position between a later-described sheet and the intermediate transfer belt 7 as the intermediate transfer belt 7 travels. 11 is transferred onto the paper.

  At this time, the intermediate transfer belt 7 and the transfer roller 11 are pressed against each other at a predetermined nip, and a voltage for transferring the toner onto the sheet is applied to the transfer roller 11 (opposite to the charging polarity (−) of the toner). Polarity (+) high voltage). Further, in order to obtain the nip constantly, the transfer roller 11 uses either the transfer roller 11 or the intermediate transfer belt drive roller 71 as a hard material (metal or the like) and the other as a soft material (elasticity such as an elastic roller). Rubber roller or foaming resin roller).

  Further, as described above, the toner adhered to the intermediate transfer belt 7 due to contact with the photosensitive drum 3 or the toner that is not transferred onto the sheet by the transfer roller 11 and remains on the intermediate transfer belt 7 Therefore, the intermediate transfer belt cleaning unit 9 removes and collects the toner. The intermediate transfer belt cleaning unit 9 includes a cleaning blade 91 as a cleaning member that comes into contact with the intermediate transfer belt 7. The intermediate transfer belt 7 contacts the intermediate transfer belt 7 in contact with the cleaning blade 91 from the back side. It is supported by a driven roller 72. The residual toner collected by the cleaning blade 91 falls and accumulates in a storage unit 92 installed below the cleaning blade 91.

  The paper feed cassette 10 is a cassette for storing sheets (recording paper) used for image formation, and is provided at the bottom of the image forming apparatus A, that is, below the exposure unit 1. The paper discharge tray 15 provided on the upper part of the image forming apparatus A is a tray for placing printed sheets face down.

  Further, the image forming apparatus A is provided with a paper transport path S for sending the sheets of the paper feed cassette 10 to the paper discharge tray 15 via the transfer roller 11 and the fixing device 12. The paper transport path S extends in a substantially vertical direction from the paper discharge unit of the paper feed cassette 10 toward the paper discharge tray 15. Further, a pickup roller 16 (16-1), a registration roller 14, a transfer roller 11, a fixing device 12, and a conveyance roller 25 (25) that conveys a sheet are provided in a paper conveyance path S from the paper cassette 10 to the paper discharge tray 15. -1,25-2, 25-3) and the like are disposed.

  The conveyance rollers 25 are small rollers for promoting and assisting conveyance of the sheet, and a plurality of conveyance rollers 25 are provided along the sheet conveyance path S. The pickup roller 16 is a drawing roller that is provided at the end of the paper feed cassette 10 and that feeds sheets one by one from the paper feed cassette 10 to the paper transport path S.

  Further, the registration roller 14 temporarily holds the sheet being conveyed on the sheet conveyance path S. The sheet has a function of conveying the sheet to a transfer unit (a nip portion between the transfer roller 11 and the intermediate transfer belt driving roller 71) at the timing when the leading edge of the toner image on the intermediate transfer belt 7 is aligned with the leading edge of the sheet. Yes.

  The fixing device 12 includes a heat roller 31, a pressure roller 32, and the like, and the heat roller 31 and the pressure roller 32 rotate with a sheet interposed therebetween. The heat roller 31 is set by the control unit to have a predetermined fixing temperature based on a signal from a temperature detector (not shown), and is transferred to the sheet by thermocompression bonding the sheet together with the pressure roller 32. The resulting multicolor toner image is melted, mixed, and pressed to thermally fix the sheet.

  The sheet after the fixing of the multicolor toner image is transported on the paper transport path S by the transport rollers 25, and is discharged onto the paper discharge tray 15 with the multicolor toner image facing downward. .

  Next, the sheet conveyance path will be described in detail. The image forming apparatus is provided with a paper feed cassette 10 that stores sheets in advance, and a manual feed tray 20 that does not need to open and close the paper feed cassette 10 when a user prints a small number of sheets. ing.

  In both paper feeding methods, pickup rollers 16 (16-1 and 16-2) are arranged, respectively, so as to guide one sheet to the conveyance path.

  The sheet conveyed from the sheet feeding cassette 10 is conveyed to the registration roller 14 by the conveying roller 25-1 in the conveying path, and is transferred to the transfer roller 11 at a timing when the leading edge of the sheet and the leading edge of the image information on the intermediate transfer belt 7 are aligned. The image information is written on the sheet. Thereafter, the sheet passes through the fixing device 12, whereby unfixed toner on the sheet is melted and fixed by heat, and is discharged from the discharge roller 25-3 onto the discharge tray 15 through the conveyance roller 25-2 ( (When requesting single-sided printing)

  On the other hand, the sheets stacked on the manual feed tray 20 are fed by the pickup roller 16-2, reach the registration roller 14 through a plurality of transport rollers (25-6, 25-5, 25-4), and thereafter. The sheet is discharged from the sheet feeding cassette 10 to the sheet discharge tray 15 through the same process as that of the sheet fed (when single-side printing is requested).

  At this time, if the print request content is a double-sided print request, the trailing edge of the sheet that has finished single-sided printing and passed through the fixing device 12 as described above is chucked by the paper discharge roller 25-3, and the paper discharge roller 25 -3 reversely rotates and is guided to the switchback conveyance path S1 provided with the conveyance rollers (25-7, 25-8), then the back side printing is performed through the registration rollers 14, and then the paper discharge tray. 15 will be discharged.

  In the actual image forming operation, the intermediate transfer roller 6 is subjected to intermediate transfer in response to a print request in order to reduce deterioration of the photosensitive drum 3 due to contact between the intermediate transfer belt 7 and the photosensitive drum 3. The intermediate transfer belt 7 and the photosensitive drum 3 can be separated from each other by moving the belt 7 in a direction in which the belt 7 is in contact with or separated from the belt 7.

  That is, the print request includes a color mode and a monochrome mode. In the color mode, each intermediate transfer roller 6 (6a to 6d) moves so as to come into contact with the back surface of the intermediate transfer belt 7, thereby performing the intermediate transfer. The surface of the belt 7 and each of the photosensitive drums 3 (3a to 3d) come into contact with each other so that the toner image of each hue can be primarily transferred to the intermediate transfer belt 7. On the other hand, in the monochrome mode, only the intermediate transfer roller 6a for black image formation moves so as to come into contact with the back surface of the intermediate transfer belt 7, thereby the surface of the intermediate transfer belt 7 and the photosensitive drum for black image formation. 3a comes into contact with the black toner image so that it can be primarily transferred to the intermediate transfer belt 7.

  As a characteristic part of the present invention, as shown in FIG. 2, an exposure unit case 1a located on an optical path Z (indicated by a broken line in the drawing) of light exposed from the exposure unit 1 toward the photosensitive drum 3 is used. Is provided with an opening 1b so as not to obstruct the optical path Z of light. The opening 1b is provided with a glass plate G as a transparent member in order to prevent the exposure unit 1 from being contaminated when the falling or scattered toner T enters through the opening 1b. In this case, the toner that falls or scatters has no electric field effect due to the flow of the wind generated from the peripheral speed of the photosensitive drum 3 and the developing sleeve SV, and the electric field of the developing sleeve SV. This can be caused by gravity falling due to gravity or flying in the plane.

  The glass plate G is provided with its photosensitive drum side surface Ga (right side surface in FIG. 2) and exposure unit side surface Gb (left side surface in FIG. 2) standing substantially perpendicular to the horizontal line, and its refractive index is 1. .7 or higher, for example, heavy flint glass (SF1). In this case, the bending rate of the glass plate G made of heavy flint glass (SF1) is 1.71736, which is for the d-line (λ = 588 nm).

  Further, the optical path Z of the light incident on the glass material G from the exposure unit 1 is refracted so as to be emitted toward the center of the photosensitive drum 3. The photosensitive drum side surface Ga of the glass plate G includes a surface coating layer C that has been subjected to a coating process that enhances the sliding property of the toner T that has fallen onto the photosensitive drum side surface Ga. As the surface coat layer C, a coating material such as fluorine is used to quickly remove rainwater dripping onto the windshield of a car. In this case, the slipperiness of the glass material G is generally represented by a water wetting angle that is an index of water repellency such as water droplets, and is enhanced by increasing the water wetting angle.

  Therefore, in the first embodiment, the glass plate G is in a horizontal line on the optical path Z of the light exposed from the exposure unit 1 toward the photosensitive drum 3, that is, on the portion (opening portion 1b) corresponding to the optical path Z from the exposure unit 1. On the other hand, the toner T that falls and scatters is blocked by the glass plate G, and contamination by the toner T in the exposure unit 1 can be reliably prevented. In addition, even if the toner T that falls or scatters falls on the glass plate G, the toner T flows downward along the photosensitive drum side surface Ga that is substantially perpendicular to the horizontal line every time it falls, and the toner that falls or scatters. T is not deposited on the glass plate G, the contamination on the optical path Z by the toner T is eliminated, and the image information can be accurately written on the photosensitive drum 3 by exposure.

  And since the glass plate G is comprised by the heavy flint glass (SF1) whose refractive index is 1.7 or more, there is a large angle difference between the incident angle and the outgoing angle of the optical path Z of the light with respect to the glass material G. The optical path Z of the light emitted from the glass material G using the angular difference of the glass material G is shortened in the horizontal direction, and the optical path Z (emitted light) of the light emitted from the glass material Z is reduced. The distance in the horizontal direction between the glass material G and the photosensitive drum 3 necessary for irradiating the photosensitive drum 3 becomes short, and the image forming apparatus A can be made compact in the horizontal direction.

  Further, since the optical path Z of the light incident on the glass material G from the exposure unit 1 is refracted so as to be emitted toward the photosensitive drum 3, the irradiation position of the image written by exposure is shifted or blurred. There is no image, and the print quality can be improved.

  Further, since the surface coating layer C is provided on the photosensitive drum side surface Ga of the glass plate G so that the coating treatment for improving the slipping property of the toner T in the inclination direction is provided, the falling and scattering toner T is removed from the glass material G. When the toner falls on the photosensitive drum side surface Ga, the toner T actively flows downward on the glass material G by the surface coat layer C, and the falling and scattering toner T is effectively deposited on the glass material G. Thus, the contamination on the optical path Z by the toner T can be more reliably eliminated, and the accuracy can be increased when the image information is written on the photosensitive drum 3 by exposure.

  Next, the structure of Example 2 of this invention is demonstrated based on FIG.

  In Example 2, the glass material is changed. In addition, the structure other than the glass material is the same as in the case of the first embodiment, and the same parts are denoted by the same reference numerals and detailed description thereof is omitted.

  That is, in this embodiment, as shown in FIG. 3, the opening on the upper surface of the exposure unit case 1a located on the optical path Z (indicated by a broken line in the figure) of light exposed from the exposure unit 1 toward the photosensitive drum 3 The portion 1b is provided with a glass plate G ′ as a transparent glass material in order to prevent the exposure unit 1 from being contaminated due to the falling or scattering toner T entering through the opening 1b. In this glass material G ′, the photosensitive drum side surface Ga ′ (right side surface in FIG. 3) stands substantially perpendicular to the horizontal line, and the lower portion of the exposure unit side surface Gb ′ (left side surface in FIG. 3) is inclined. It is formed in a prism shape.

  The glass plate G ′ is made of a high refractive index material having a refractive index of 1.7 or more, such as heavy flint glass (SF1). The light path Z of the light incident on the glass material G ′ from the exposure unit 1 is refracted so as to be emitted toward the photosensitive drum 3. Further, the photosensitive drum side surface Ga ′ of the glass plate G ′ includes a surface coating layer C that has been subjected to a coating process that enhances the sliding property of the toner T that has fallen onto the photosensitive drum side surface Ga ′. .

  Therefore, in the second embodiment, a transparent glass material G ′ is formed on the optical path Z of the light exposed from the exposure unit 1 toward the photosensitive drum 3, that is, on the portion corresponding to the optical path Z from the exposure unit 1 (opening 1 b). Therefore, the toner T that falls and scatters is blocked by the glass material G ′, so that contamination by the toner T in the exposure unit 1 can be surely prevented. In this case, the glass material G ′ is formed in a prism shape in which the photosensitive drum side surface Ga ′ stands up substantially perpendicular to the horizontal line and the exposure unit side surface Gb ′ is inclined. Even when the glass material G ′ falls on the photosensitive drum side surface Ga ′, each time it falls, the toner T flows downward on the photosensitive drum side surface Ga ′ of the glass material G ′, and the toner T that falls and scatters is dropped. The glass material G ′ is not deposited on the side surface Ga ′ of the photosensitive drum, the contamination on the optical path Z by the toner T is eliminated, and the image information can be accurately written on the photosensitive drum 3 by exposure.

  Further, the prism-shaped glass material G ′ made of a high refractive index material (heavy flint glass) has a larger angle difference between the incident angle and the outgoing angle of the optical path Z of the light with respect to the glass material G ′. The optical path Z of the light emitted from the glass material G ′ is effectively shortened in the horizontal direction by utilizing the large angle difference of the material G ′, and the optical path Z (emitted light) of the light emitted from the glass material G ′. The horizontal distance between the glass material G ′ and the photosensitive drum 3 required for irradiating the photosensitive drum 3 with the photosensitive drum 3 is greatly shortened, a marginal area is generated in the optical path design, and the horizontal direction of the image forming apparatus A is increased. Further downsizing in the direction can be achieved.

  In addition, this invention is not limited to said each Example, Other various modifications are included. For example, in each of the above-described embodiments, the glass materials G and G ′ are made of heavy flint glass (SF1). However, the present invention is not limited to this. If the refractive index is 1.7 or more, resin (plastic) Of course, the transparent member may be made of any high refractive index material.

  Furthermore, in the above-described embodiment, the case where the present invention is applied to the image forming apparatus A configured as a color printer has been described. However, the present invention is not limited thereto, and an image forming apparatus configured as a color copying machine, The present invention is also applicable to an image forming apparatus configured as a multifunction machine having the above functions.

1 is a diagram illustrating an internal configuration of an image forming apparatus according to Embodiment 1 of the present invention. It is explanatory drawing explaining the arrangement | positioning state of the glass material in the vicinity of the opening part of the exposure unit case upper surface located on the optical path of the light similarly exposed toward a photosensitive drum from an exposure unit. It is explanatory drawing explaining the arrangement | positioning state of the glass material in the vicinity of the opening part of the exposure unit case upper surface located on the optical path of the light exposed toward the photosensitive drum from the exposure unit concerning Example 2 of this invention.

Explanation of symbols

1 Exposure unit 21 (21a-21d)
Developer tank 3 (3a-3d)
Photosensitive drum (image carrier)
A Image forming apparatus C Surface coat layer G, G 'Glass material (transparent member)
Ga, Ga '
Photosensitive drum side surface (image carrier side surface)
Gb, Gb ′
Side of exposure unit T Toner (Developer)
Z optical path of light

Claims (3)

An exposure unit for writing the electrostatic latent image on the image carrier by exposure is disposed below a developing tank containing a developer that develops the electrostatic latent image formed on the image carrier into a visible image. In the formed image forming apparatus,
On the optical path of the light that is exposed from the exposure unit toward the image carrier, a transparent member that prevents the exposure unit from being soiled due to the falling or scattering of the developer is provided to stand substantially perpendicular to the horizontal line. And
The image forming apparatus, wherein the transparent member is made of a material having a high refractive index. An exposure unit for writing the electrostatic latent image on the image carrier by exposure is disposed below a developing tank containing a developer that develops the electrostatic latent image formed on the image carrier into a visible image. In the formed image forming apparatus,
On the optical path of the light that is exposed from the exposure unit toward the image carrier, a transparent member that prevents the exposure unit from being contaminated by the falling or scattering of the developer is provided.
2. The image forming apparatus according to claim 1, wherein the transparent member is formed in a prism shape in which the side surface of the image carrier stands substantially perpendicular to the horizontal line and the side surface of the exposure unit is inclined. In the image forming apparatus according to claim 1 or 2,
An image forming apparatus, wherein a side surface of an image carrier of a transparent member is provided with a surface coating layer that has been subjected to a coating process that enhances the downward sliding property of a developer dropped on the side surface of the image carrier.

Images