JP2007187805A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a contact charging system image forming apparatus, using an amorphous silicon photosensitive drum, in which the surface potential of the photosensitive drum is kept substantially fixed in the axial direction of the photosensitive drum. <P>SOLUTION: Charge-removing light is guided by an optical path defining member 623, when the amorphous silicon photosensitive drum 2 is irradiated with the charge removing light from a charge removing unit 6. The optical path defining member 623 is configured so that a first reflector 623A as a reflector, having low reflectance, serves as a base member and a second reflector 623B as a reflector, having high reflectance, is stuck on the base member. The second reflector 623B is set wide in portions, corresponding to both end portions in the axial direction of the photosensitive drum 2 and becomes gradually narrower as going toward the center portion in the axial direction. Thus, the amount of the charge removing light, applied to the center portion in the axial direction of the photosensitive drum 2, is reduced comparatively to compensate surface potential irregularities, caused by the nip width between the photosensitive drum 2 and a charging roller 31 being different in the axial direction and to uniformize the surface potential. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus for charging a photosensitive drum using a predetermined photosensitive member, particularly an amorphous silicon (a-Si) photosensitive member, by a contact charging method.

  Conventionally, as a device for charging a drum-type electrophotographic photosensitive member (hereinafter simply referred to as a photosensitive drum), a corona charging device that charges a discharge corona by exposing it to the surface of the photosensitive drum has been used. Since it has advantages such as low ozone and low power compared to the device, an image forming device that employs a contact charging method in which a charging member (charging roller, etc.) to which a voltage is applied is brought into contact with the surface of the photosensitive drum for charging is practical. (For example, refer to Patent Document 1).

On the other hand, selenium and OPC (Organic Photo Conductor) have been conventionally used as the material for the surface of the photosensitive drum. However, in recent years, from the viewpoints of environmental problems, longer life, etc., amorphous silicon (a-Si) photoreceptors have been used. Are beginning to be used.
JP-A-8-272270

  However, the contact charging method has the following problems. That is, in order to realize the contact charging method, a method is generally employed in which a conductive rubber roller (charging roller) containing an ionic conductive agent is pressed against the photosensitive drum, but when the charging roller is pressed against the photosensitive drum. In addition, the load at the central portion in the axial direction of the photosensitive drum is inevitably smaller than both ends, and the nip width between the photosensitive drum and the charging roller is smaller at the central portion than both ends. As a result, the charged potential at the central portion in the axial direction of the photosensitive drum is lower than both ends in the axial direction, and the surface potential of the photosensitive drum may become uneven, causing image disturbance such as fogging. In order to solve such a problem, a technique for suppressing unevenness of the surface potential due to the nip width difference is known by using a bias in which an AC voltage is superimposed on a DC voltage as a bias applied to the charging roller. .

  However, in the case of a photosensitive drum using an amorphous silicon photosensitive member, the influence of the nip width between the charging roller and the photosensitive drum is large, and even a slight difference in the nip width greatly affects the surface potential. This is due to the fact that the amorphous silicon photoconductor has a lower charging capability than an organic photoconductor such as OPC. For this reason, in the image forming apparatus using the amorphous silicon photosensitive drum, the unevenness of the surface potential cannot be sufficiently eliminated even with the method of superimposing the AC bias described above, and a problem such as fogging may occur.

  The present invention has been made in view of the above circumstances, and in a contact charging type image forming apparatus using a predetermined photosensitive member, particularly an amorphous silicon photosensitive drum, the surface potential of the photosensitive drum is kept substantially constant in the axial direction thereof. An object of the present invention is to provide an image forming apparatus and a charge eliminating method that can prevent occurrence of problems such as fogging.

  The image forming apparatus according to claim 1 is an image forming apparatus that forms an image by transferring a toner image onto a predetermined transfer material, and is rotatably supported by an electrostatic latent image formed on the surface thereof. A photosensitive member on which the toner image is formed by attaching toner to the electrostatic latent image, a charging means by a contact charging method for charging the photosensitive member, and the toner image from the surface of the photosensitive member to the transfer material. A neutralizing unit that neutralizes the surface of the photosensitive member after the transfer, and the neutralizing unit includes a linear light source that emits predetermined neutralizing light, a linear incident end disposed toward the light source, and a linear output. A light guide member that is arranged toward the surface of the photoconductor and irradiates the surface of the photoconductor with a line in a line shape, and the light guide member is at least from the incident end to the output end. With respect to the central portion in the rotational axis direction of the photoconductor The neutralizing light to be irradiated is transmitted with a predetermined first light guide characteristic, and a second light guide characteristic with less light guide loss than the first light guide characteristic with respect to the rotation axis direction end portion of the photoconductor. It is configured to transmit static elimination light.

  For example, an amorphous silicon photoconductor has a characteristic that the amount of excited photocarriers generated varies depending on the amount of static elimination light applied to remove charges. That is, as the charge removal amount increases, the amount of generated photocarriers increases, and the number of photocarriers trapped inside the amorphous silicon photosensitive layer tends to increase. The trapped optical carrier has a function of neutralizing the charge received from the charger (charging roller) in the charging stage, thereby reducing the surface potential of the photoreceptor. This means that the charge potential at the charging stage can be adjusted by controlling the amount of charge removed on the amorphous silicon photoconductor.

  Focusing on this point, in the present invention, the light guide characteristics of the static elimination light in the light guide member are transmitted to the central portion of the photosensitive member in the rotation axis direction and the static elimination light to the rotation axis direction end. The amount of static elimination applied to the surface of the photoconductor is made different by making the portion different. That is, the static elimination light is transmitted to the central portion in the rotation axis direction of the photosensitive member with a predetermined first light guide characteristic, and the light guide loss is more than the first light guide characteristic to the end portion in the rotation axis direction. By using a light guide member that transmits static elimination light with a small second light guide characteristic, a relatively large amount of static elimination light is given to the end portion in the rotation axis direction than the central portion in the rotation axis direction of the photoreceptor. Yes. That is, the amount of charge removal is reduced at the central portion in the rotation axis direction of the photoconductor, compared to the end portion in the rotation axis direction, and the generation amount of the optical carrier is suppressed as compared with the end portion in the rotation axis direction. As a result, the degree of charge neutralization by the charging stage at the central portion in the rotational axis direction of the photosensitive member is reduced, and a state in which the charging potential can be relatively increased at the central portion in the rotational axis direction than at the end portion is formed. It will be. Therefore, even if the nip width between the photoconductor and the charging roller as the charging means is smaller at the center than at both ends in the rotation axis direction, it is offset by the difference in the amount of generated photocarriers, and the surface potential of the photoconductor is made uniform. Become so.

  In the above configuration, the light guide member includes a pair of flat plate members that form a slit-shaped light transmission space between the line light source and the photoconductor, and the light transmission of at least one of the flat plate members. The first light guide is on the first shortest line connecting at least the central portion in the width direction of the line-shaped light source and the central portion in the rotation axis direction of the photosensitive member at a surface facing the space. On the second shortest line connecting the vicinity of the end in the width direction of the line light source and the vicinity of the end in the rotation axis direction of the photoconductor, the second light guide characteristic is obtained. It can be set as the structure made into the 2nd reflectance which implement | achieves (Claim 2).

  According to this configuration, the static elimination light is transmitted to the photoconductor while reflecting the slit-like light transmission space of the light guide member made of a pair of flat plate members in a multiple manner. The first shortest line connecting the vicinity of the central portion in the width direction of the linear light source and the vicinity of the central portion in the rotation axis direction of the photosensitive member on the surface of at least one of the flat plate-like members facing the light transmission space. The first light guide characteristic and the second light guide characteristic are made different on the line and on the second shortest line connecting the vicinity of the end in the width direction of the linear light source and the vicinity of the end in the rotation axis direction of the photosensitive member. Is realized. In other words, the first shortest line has a first reflectance that realizes a first light guide characteristic, and the second shortest line has a second reflectance that realizes a second light guide characteristic. A light guide member is used. Here, as described above, since the second light guide characteristic is a characteristic with less light guide loss than the first light guide characteristic, the second reflectivity is higher than the first reflectivity. Become a rate. As a result, the amount of static elimination applied to the end of the photosensitive member in the rotation axis direction becomes relatively large, and the optical carrier can be generated so that the influence of the nip width can be reduced or offset.

  The said structure WHEREIN: It is desirable to set it as the structure by which the surface facing the said optical transmission space of the said flat member is comprised by the combination of the 1st reflector and 2nd reflector from which reflectance differs. Item 3). According to this configuration, it is possible to form a reflecting surface having the first reflectance and the second reflectance by appropriately combining the first reflector and the second reflector having different reflectances. It becomes.

  In this case, the first reflector is a reflector having a low reflectance, the second reflector is a reflector having a high reflectance, and the first reflector is used as a base member. It is desirable that the second reflector is affixed in a shape having the smallest area on the first shortest line and the largest area on the second shortest line (claim 4). In this case, it is desirable that the second reflector has a shape in which the occupied area gradually decreases from the large area portion on the second shortest line toward the small area portion on the first shortest line ( Claim 5). According to this configuration, the first reflector, which is a reflector having a low reflectance, is used as a base member, and the pasting shape of the second reflector, which is a reflector having a high reflectance, is set on the first shortest line and the second shortest line. By making the line different from each other, it is possible to easily form the reflection surface having the first reflectance and the second reflectance.

  In any one of the above configurations, it is desirable that the photoconductor is made of a photoconductor using amorphous silicon.

  According to the first aspect of the present invention, when a contact charging method in which the photosensitive member is charged using a charging roller or the like is employed, the surface generated due to a difference in nip width between the charging roller or the like and the photosensitive member. Potential unevenness, that is, the phenomenon that the surface potential of the central portion in the rotation axis direction of the photoconductor is inevitably lower than that of the end portion can be avoided by controlling the generation amount of light carriers in the rotation axis direction of the photoconductor. become. Therefore, for example, in a contact charging type image forming apparatus using an amorphous silicon photosensitive drum, it is possible to prevent image disturbance such as fogging due to uneven surface potential.

  According to the second aspect of the present invention, the light guide member is composed of a pair of flat plate-like members, and the neutralization light reflectance thereof is determined in the vicinity of the central portion in the width direction of the linear light source and the central portion in the rotational axis direction of the photosensitive member. Neutralization applied to the photosensitive member with a simple configuration in which it is different on the first shortest line connecting the two and the second shortest line connecting the vicinity of the end of the linear light source in the width direction and the end of the photosensitive member in the rotation axis direction. The amount of light can be adjusted in the direction of the rotation axis.

  According to the invention described in claim 3, since the reflectance is adjusted by the combination of the first reflector and the second reflector having different reflectances, the configuration of the light guide member can be simplified and the cost can be reduced. Can be achieved.

  According to the fourth aspect of the present invention, the desired reflection can be achieved simply by selecting the pasting shape of the second reflector that is a reflector having a high reflectivity with respect to the first reflector that is a reflector having a low reflectivity. It is possible to easily form a reflective surface having a rate.

  According to the fifth aspect of the present invention, the light guide characteristic can be gradually changed from the rotation axis direction end portion of the photoconductor toward the rotation axis direction central portion, and the amount of charge removed on the surface of the photoconductor is further increased. It becomes possible to optimize.

  According to the sixth aspect of the present invention, since the photoconductor using amorphous silicon is used as the photoconductor, the effect of adjusting the amount of charge removed according to the present invention can be enjoyed more remarkably.

  Hereinafter, an example of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a schematic configuration of an image forming apparatus according to the present invention. Although the case where the image forming apparatus is a copying machine will be described here, other image forming apparatuses (for example, a facsimile, a printer, a scanner, etc.) may be used.

  As shown in FIG. 1, the copying machine 1 generally includes a copying machine main body 100 and a document reading unit 110. The copying machine main body 100 includes a paper feeding mechanism 11, a paper transport path 101, an image forming unit 200, a fixing unit 300, a toner container 400, and the like.

  The paper feed mechanism 11 is configured to be detachable from the copying machine main body 100, and includes paper feed cassettes 111 and 112 for storing paper, and a stack bypass (bypass tray) 113 disposed above them. Is connected to the image forming unit 200 via the paper conveyance path 101.

  The image forming unit 200 transfers a toner image onto a predetermined sheet (transfer material) to form an image, and a photosensitive drum 2 (on the photosensitive member) using an amorphous silicon photosensitive member rotating in the direction of arrow A in the figure. And a charging unit 3 (corresponding to a charging means) of a contact charging method for charging the surface of the photosensitive drum 2 substantially uniformly, and an electrostatic latent image corresponding to the original image on the surface of the photosensitive drum 2 with a laser beam. An exposure unit 4 formed by a laser scanning unit, a developing unit 5 that forms a toner image by attaching a developer (hereinafter referred to as toner) to the formed electrostatic latent image by a developing roller 51, and a photosensitive drum. A transfer roller 21 for transferring the toner image formed on the surface 2 to the paper, and a static elimination unit 6 (corresponding to a static elimination means) for eliminating the surface of the photosensitive drum 2 after the toner image is transferred to the paper. ) And is configured by a cleaning blade 7 for removing toner adhering to the surface of the photosensitive drum 2 after the transfer.

  The fixing unit 300 is configured to include a pair of fixing rollers for separating the paper on which the toner image is transferred from the photosensitive drum 2 and fixing the toner image on the paper. The toner container 400 is for supplying toner to the developing unit 5.

  The document reading unit 110 is a so-called scanner unit for reading an image of a document to obtain image data. The document reading unit 110 is a contact glass (platen glass) made of a transparent member such as glass on which the document is placed, and irradiates the document with light. A mirror unit formed by integrating an exposure lamp, which is a light source, and a mirror that reflects the reflected light from the document, a lens group that squeezes the reflected light from the mirror unit, and the reflected light is focused by the lens group to form an image. A CCD image sensor including an image pickup device (CCD: charge coupled device) that photoelectrically converts an optical image to obtain image data is provided.

  In addition, the copying machine 1 includes a paper sorting unit 104 that sorts the transport direction by a branch member with respect to the paper that has passed through the fixing unit 300, a paper transport path 105 through which paper is transported during duplex copying, and discharged paper. An upper sheet tray 102a, a lower sheet tray 102b, a sheet tray 103, and the like.

  FIG. 2 is a schematic diagram illustrating an example of a schematic configuration of the image forming unit 200. The image forming unit 200 that forms an image on the sheet S includes a charging unit 3, an exposure unit 4, a developing unit 5, and a transfer roller 21 around the photosensitive drum 2 from the upstream side in the rotation direction indicated by an arrow A in the drawing. The static eliminating unit 6, the polishing roller 22 (not shown in FIG. 1), and the cleaning blade 7 are sequentially arranged.

  The photosensitive drum 2 is for forming an electrostatic latent image on the peripheral surface. The drum body 201 is a cylindrical body made of a predetermined metal material (for example, aluminum having a diameter of 30 mm), and the drum body 201 An amorphous silicon layer 202 formed by laminating amorphous silicon photoreceptors formed by vapor deposition, for example, on the peripheral surface, and is rotatable about a rotation axis 203 at a predetermined peripheral speed (for example, 175 mm / sec). It is supported.

  The amorphous silicon layer 202 is formed by solidifying a silica (Si) or a silica compound (SiC, SiO, SiON, etc.) in a solid solution, and is usually formed by a physical vapor deposition process such as a sputtering process. Such an amorphous silicon layer 202 (particularly made of SiC) has excellent charging ability due to its high resistance, and also has excellent wear resistance and environmental resistance, and is a material for forming an electrostatic latent image. Is preferred.

  The charging unit 3 uses a contact charging method to charge the surface of the photosensitive drum 2 substantially uniformly. The charging unit 31 includes a cored bar, an outer peripheral conductive layer, and an outer peripheral resistance layer. Have Further, a bearing 32 that rotatably supports the charging roller 31 at both ends, and a biasing force is applied to the bearings 32 disposed at both ends so that the surface of the charging roller 31 is applied to the surface of the photosensitive drum 2 with a predetermined pressure. A pressure spring 33 that is held in contact with the charging roller 31 and a power source (not shown) that applies a predetermined voltage (for example, a DC voltage superimposed with an AC voltage) to the charging roller 31 are provided. That is, the charging roller 31 is formed of a conductive rubber material or foaming synthetic resin with a predetermined elasticity, and the peripheral surface of the charging roller 31 is in contact with the peripheral surface of the rotating photosensitive drum 2. The surface potential of the photosensitive drum 2 is raised by applying a predetermined voltage from the power source.

  The exposure unit 4 includes an LED print head (for example, having a number of pixels of 7168 in the line direction) disposed on the downstream side of the charging unit 3 and facing the peripheral surface of the photosensitive drum 2. Laser light from the print head is irradiated onto the peripheral surface of the photosensitive drum 2 to generate an electrostatic latent image.

  The developing unit 5 forms a toner image by attaching toner to the electrostatic latent image formed on the surface of the photosensitive drum 2 by the exposure unit 4, and is a monochrome one-component jumping method here.

  The transfer roller 21 peels off the toner image from the surface of the photosensitive drum 2 (amorphous silicon layer 202) by applying a polarity opposite to the polarity of the charge of the toner image formed on the peripheral surface of the photosensitive drum 2, and transfers the transfer roller. 21 is transferred onto the sheet S being conveyed between the peripheral surface 21 and the photosensitive drum 2.

  The static elimination unit 6 (static elimination means) removes charges such as an electrostatic latent image formed on the surface of the photosensitive drum 2 by the exposure unit 4 by irradiating predetermined static elimination light. An array 61 (line-shaped light source) and a line-shaped incident end 621 are disposed toward the LED array 61, and a line-shaped emission end 622 is disposed toward the surface of the photosensitive drum 2. And a light guide member 62 that irradiates the two axial surfaces in a line. The configuration of the static elimination unit 6 will be described in detail later.

  The polishing roller 22 is formed of a synthetic resin material that can be elastically deformed and has excellent toughness, and polishes and cleans the amorphous silicon layer 202 on the surface of the photosensitive drum 2. The polishing roller 22 is rotated in the direction opposite to the photosensitive drum 2 (counterclockwise in the example shown in FIG. 2) at a peripheral speed faster than the peripheral speed of the photosensitive drum 2 around its axis. As a result, discharge products and residual toner adhering to the amorphous silicon layer 202 are scraped off, and the amorphous silicon layer 202 is cleaned.

  The cleaning blade 7 is a finishing cleaning member for the peripheral surface of the photosensitive drum 2 and is formed in a plate shape by an elastic material such as rubber. The cleaning blade 7 is in contact with the amorphous silicon layer 202 at the tip end of the cleaning blade 7 in a state of being inclined downward toward the circumferential surface of the photosensitive drum 2. Therefore, in accordance with the rotation of the photosensitive drum 2 in the direction of arrow A, deposits that could not be removed by the polishing roller 22 are scraped off by the cleaning blade 7. The deposits (discharge products and residual toner) removed by the polishing roller 22 and the cleaning blade 7 are collected in a not-shown collection bottle provided in the copying machine main body 100.

  Next, the configuration of the static elimination unit 6 will be described in detail. FIG. 3 is a partially broken perspective view showing the configuration of the static elimination unit 6 in the arrangement relationship with the photosensitive drum 2. This static elimination unit 6 is comprised by the LED array 61 and the light guide member 62 as a linear light source as above-mentioned. The LED array 61 includes an elongated rod-shaped LED holder 611 and a plurality of LEDs 612 arranged on the LED holder 611 at a predetermined interval. The LED 612 is an edge-emitting semiconductor light-emitting element that emits light of a predetermined wavelength (charge eliminating light) having a charge eliminating ability.

  The light guide member 62 is composed of a pair of flat plate members that form a slit-shaped light transmission space P. In this embodiment, a slit-shaped light transmission space P is formed in the light emitting direction of the LED array 61 using a predetermined optical path securing member 623 and a frame member 106 for incorporating the photosensitive drum 2. Yes. The frame member 106 is made of SUS sheet metal or the like, and is a flat plate member having a width at least equal to the axial size of the rotating shaft 203 of the photosensitive drum 2. The optical path securing member 623 is made of a film member whose reflectance is adjusted to a predetermined value, and is similarly a flat plate member having a width at least equal to the axial size of the rotating shaft 203 of the photosensitive drum 2.

  A slit-shaped light transmission space P is formed by sandwiching the LED array 61 from above and below by such two flat plate members of the frame member 106 and the optical path securing member 623. Then, the static elimination light OP emitted from each LED 612 of the LED array 61 propagates in the light transmission space P and is guided to the vicinity of the photosensitive drum 2, and is lined from the emitting end 622 to the axial surface of the photosensitive drum 2. Irradiated in a shape. Residual charges after transfer are removed by the irradiation of the charge eliminating light OP.

  In the static elimination unit 6 configured as described above, the static elimination light reflectance of the surface of the frame member 106 forming the slit-like optical transmission space P facing the optical transmission space P is substantially uniform. On the other hand, the optical path securing member 623 has a static elimination light reflectance on the surface facing the light transmission space P in order to vary the amount of static elimination light applied to the surface of the photosensitive drum 2 in the axial direction of the photosensitive drum 2. It is partly different.

  This point will be specifically described with reference to FIG. FIG. 4 is a schematic diagram showing a planar view of the state as seen from the direction of arrow B in FIG. In FIG. 4, the portion of the static elimination unit 6 is drawn excluding the frame member 106. As shown in the figure, the optical path securing member 623 has a first reflector 623A having a relatively low reflectivity (for example, a static elimination light reflectivity of 50% or less) as a base member, and is a surface facing the optical transmission space P. A second reflector 623B having a relatively high reflectivity (for example, a static elimination light reflectivity of 85% or more) is attached to the top. For example, a black matte film having a 660 nm wavelength neutralizing light reflectance of 38% is used as the first reflector 623A, and a silver aluminum film having a 660 nm wavelength neutralizing light reflectance is 95% as the second reflector 623B. Tape can be used.

  The second reflector 623B has the widest portion corresponding to the axial end (rotational axis end) of the photosensitive drum 2 and the widest portion corresponding to the axial central portion (rotational axial center). It is a narrow right-angled triangle. That is, on the surface of the optical path securing member 623 that faces the light transmission space P, as shown in FIG. 5A, the portion of the second reflector 623B having a high reflectance at the portion corresponding to the end in the axial direction of the photosensitive drum 2 The occupied area is the largest, and the occupied area of the second reflector 623B gradually decreases toward the central portion in the axial direction. As shown in FIG. 5B, the second reflector 623B has an occupied area in the central portion in the axial direction. The shape occupies the smallest area (configured only with the first reflector 623A).

  As a result, on the first shortest line L1 connecting the vicinity of the center portion in the width direction of the LED array 61 and the vicinity of the center portion in the axial direction of the photosensitive drum 2, the vicinity of both end portions in the width direction of the LED array 61 and the end in the axial direction of the photosensitive drum 2. On the second shortest line L2 connecting the vicinity of the portion, the light guide characteristics of the static elimination light are different. That is, the reflectance of the surface facing the light transmission space P of the optical path securing member 623 (the first reflectance) in which the second reflector 623B having a high reflectance occupies a large proportion on the first shortest line L1. On the second shortest line L2, the first reflectance 623A having a low reflectance accounts for a large proportion (second reflectance).

  With this configuration, the light guide characteristic from the incident end 621 to the exit end 622 of the light guide member 62 is such that the light guide loss of the static elimination light is relatively large on the first shortest line L1. Characteristic (first light guide characteristic), and on the second shortest line L2, the light guide characteristic (second light guide characteristic) with relatively little light guide loss of the static elimination light is obtained (see FIG. 5). As a result, the amount of static elimination applied to the central portion in the axial direction is smaller than that in the axial end portion of the photosensitive drum 2.

  As described above, since the amorphous silicon photoconductor has a characteristic that the amount of generated photocarriers increases as the amount of static elimination increases, in the central portion in the axial direction corresponding to the first shortest line L1 of the photosensitive drum 2. The optical carriers generated in the amorphous silicon layer 202 are relatively few. On the other hand, at the end in the axial direction corresponding to the second shortest line L2, a large amount of charge is given, so that the amount of generated optical carriers increases.

  In the present embodiment, such a configuration is adopted for the following reason. As shown in FIG. 4, when the contact charging method is used using the charging roller 31 or the like, in order to bring the charging roller 31 into contact with the photosensitive drum 2 with a pressing force, a pressing force is applied to the roller body portion. Therefore, a pressing method of biasing the bearings 32 at both ends with the pressure springs 33 must be taken. However, with such a pressing method, the load at the central portion in the axial direction of the photosensitive drum 2 is inevitably smaller than both ends, and the nip width between the photosensitive member and the charging roller is smaller at the central portion C1 than at both ends C2. . As a result, the surface potential (charging potential) at the central portion in the axial direction of the photosensitive drum becomes lower than both end portions in the axial direction.

  FIG. 6 shows an example of the surface potential distribution when the photosensitive drum 2 having an axial length of about 300 mm is charged by bringing the charging roller 31 applied with a pressing force at both ends thereof into contact with the photosensitive drum 2. FIG. As can be seen from FIG. 6, the surface potential of the central portion in the axial direction of the photosensitive drum 2 (the axial position = 0 mm point) is about 15 V lower than both end portions. If such a potential gradient exists, a defect such as so-called fog may appear in the formed image. The difference in nip width can be alleviated by increasing the strength of the core of the charging roller 31 or extremely reducing the rubber hardness of the conductive rubber layer, but the nip width difference is completely eliminated. In the photosensitive drum 2 using the amorphous silicon photosensitive member having a small charging ability, surface potential unevenness often appears.

  Therefore, in the present embodiment, as shown in FIG. 4, in the surface of the optical path securing member 623 that faces the light transmission space P, the first portion with low reflectivity is transmitted at the portion that transmits static elimination light to the central portion in the axial direction of the photosensitive drum 2. A portion for transmitting static electricity to the axial end of the photosensitive drum 2 by making the transmission loss of the static elimination light (synonymous with light guide loss) relatively small to reduce the quantity of static elimination light. Then, the area occupied by the second reflector 623B having a high reflectivity is increased to relatively reduce the transmission loss of the static elimination light, thereby increasing the static elimination light amount.

  That is, as shown in FIG. 7, when the photosensitive drum 2 is charged by the contact charging method using the charging roller 31, the amount of static elimination is reduced at the central portion in the axial direction where the surface potential decreases, and the amount of generated optical carriers is regulated. Thus, the neutralizing action of the charged charge is suppressed. On the other hand, a relatively large amount of static elimination light is applied to the end portion in the axial direction, and the amount of generated photocarriers is increased, so that the degree of decrease in the surface potential due to the neutralization effect of the charged charge is relatively increased.

  In this way, in the static elimination unit 6, a state is formed in which the amount of photocarrier generation in the amorphous silicon layer 202 of the photosensitive drum 2 is varied in the axial direction as described above, and then the photosensitive roller 31 of the charging unit 3 performs photosensitivity. If the drum 2 is charged, the charged potential rises because the amount of light carriers generated is smaller in the center than at both ends in the axial direction. Therefore, the surface potential unevenness caused by the difference in the nip width between the photosensitive drum 2 and the charging roller 31 in the axial direction is canceled, and as a result, the surface potential unevenness does not occur. FIG. 8 is a graph showing the axial surface potential of the photosensitive drum 2 after passing through the charging roller 31 in this embodiment. As is clear from FIG. 8, the surface potential is flat without unevenness in the axial direction.

As mentioned above, although embodiment was described about this invention, this invention is not limited to this, For example, the following aspects can be taken.
(1) In the present embodiment, the case where the image forming apparatus is the copying machine 1 has been described. However, another type of image forming apparatus (for example, a facsimile, a printer, or the like) may be used.

  (2) In the present embodiment, the optical path securing member 623 is configured by a combination of the first reflector 623A having a relatively low reflectance and the second reflector 623B having a relatively high reflectance, so that the photosensitive drum Although the example in which the transmission loss of the static elimination light at the axial central portion 2 is larger than that at the axial end portion is shown, the light guiding characteristics are different between the axial central portion and the axial end portion of the photosensitive drum 2. Various methods can be adopted. For example, an optical component that increases the transmission loss of the static elimination light may be disposed in the slit-shaped light transmission space P at the center in the axial direction of the photosensitive drum 2.

  (3) As in this embodiment, in addition to the mode of forming the slit-shaped light transmission space P, for example, a light guide film or a light guide plate having light guiding properties is used, and the incident end of the LED array is set to the LED array. Alternatively, the light emitting end may be opposed to the surface of the photosensitive drum 2. In this case, for example, in order to increase the transmission loss of the neutralizing light applied to the central portion in the axial direction of the photosensitive drum 2, particles having a light absorptivity in a portion corresponding to the transmission path portion of the light guide film or the light guide plate Etc. may be dispersed and blended.

  (4) In the present embodiment, the light guide characteristic of the optical path securing member 623 is exemplified as an aspect in which the light guide characteristic is gradually changed from the both axial ends of the photosensitive drum 2 toward the central portion. It may be an aspect that changes in a step shape from the center toward the center.

  (5) In the present embodiment, a black matte film with a 660 nm wavelength neutralizing light reflectance of 38% is used as the first reflector 623A, and a neutralizing light reflectance with a wavelength of 660 nm is 95 as the second reflector 623B. However, these are merely examples, and various low-reflective materials or high-reflective materials can be applied as the first reflector 623A and the second reflector 623B. For example, instead of the silver aluminum tape, a composite tape in which a PET film is attached on both sides of a silver film can be used. In addition, it is desirable to use a material with as little wavelength dependence as possible, but even a material with wavelength dependence can ensure a predetermined reflectance with respect to light in the band of approximately 500 nm to 700 nm. Can be used.

  (6) In the present embodiment, the photosensitive drum 2 is exemplified as the photosensitive member. However, for example, a belt-shaped photosensitive member can be used instead. In this case, the belt-like photosensitive member is rotatably supported by a driving system including a predetermined driving roller and a driven roller, and is rotationally driven (circularly driven) by the driving roller. Even in such a configuration, for example, the light guide characteristic of the optical path securing member 623 is gradually changed from both ends of the drive roller in the rotation axis direction (which becomes the rotation axis of the belt-shaped photosensitive member) toward the center portion. It ’s fine.

1 is a schematic diagram illustrating an example of a schematic configuration of an image forming apparatus according to the present invention. It is a schematic diagram which shows an example of schematic structure of an image formation part. FIG. 3 is a partially broken perspective view illustrating a configuration of a static elimination unit in an arrangement relationship with a photosensitive drum. It is the schematic diagram which showed the arrow view state from the arrow B direction of FIG. It is sectional drawing of an optical path securing member, Comprising: (a) is the L2 line shown in FIG. 4, (b) is sectional drawing of a L1 line. 6 is a graph showing a surface potential distribution in the photosensitive drum axial direction when charged by a charging roller. It is a graph which shows the static electricity irradiation amount distribution of the photosensitive drum axial direction at the time of employ | adopting this embodiment. 6 is a graph showing a surface potential distribution in the axial direction of the photosensitive drum when charged by a charging roller when this embodiment is employed.

Explanation of symbols

1 Copying machine (image forming device)
2 Photosensitive drum (photoconductor)
202 Amorphous silicon layer 203 Rotating shaft 21 Transfer roller 3 Charging unit (charging means by contact charging method)
31 Charging roller 4 Exposure unit 5 Development unit 6 Static elimination unit (static elimination means)
61 linear light source 62 light guide member 621 incident end 622 exit end 623 optical path securing member 623A first reflector (reflector with low reflectivity)
623B Second reflector (reflector with high reflectivity)
7 Cleaning blade P Optical transmission space OP Static elimination light L1 First shortest line L2 Second shortest line

Claims (6)

An image forming apparatus for transferring a toner image to a predetermined transfer material to form an image,
A photosensitive member that is rotatably supported and forms an electrostatic latent image on the surface thereof, and a toner image is formed by attaching toner to the electrostatic latent image, and a contact charging method for charging the photosensitive member. Charging means; and charge eliminating means for discharging the surface of the photosensitive member after transferring the toner image from the surface of the photosensitive member to the transfer material,
The charge eliminating means includes a line-shaped light source that emits predetermined charge-removing light, a line-shaped incident end disposed toward the light source, and a line-shaped emission end disposed toward the photoreceptor surface. A light guide member that irradiates the surface of the photoconductor in a line,
The light guide member transmits, from the incident end to the output end, at least a central portion of the photosensitive member in the rotation axis direction with a predetermined first light guide characteristic, and the rotation shaft of the photosensitive member. An image forming apparatus configured to transmit static elimination light with a second light guide characteristic with less light guide loss than the first light guide characteristic with respect to a direction end. The light guide member includes a pair of flat plate-like members that form a slit-shaped light transmission space between the line-shaped light source and the photoconductor,
The charge removal light reflectance of the surface facing the light transmission space of at least one of the flat plate members is
At least on the first shortest line connecting the vicinity of the center in the width direction of the line light source and the vicinity of the center in the rotation axis direction of the photoconductor, the first reflectance that achieves the first light guide characteristic is set.
On the second shortest line connecting the vicinity of the end of the line light source in the width direction and the vicinity of the end of the photosensitive member in the rotation axis direction, the second reflectance that realizes the second light guide characteristic is set. The image forming apparatus according to claim 1.   3. The image according to claim 2, wherein a surface of the flat plate-like member facing the light transmission space is configured by a combination of a first reflector and a second reflector having different reflectivities. Forming equipment. The first reflector is a low-reflectivity reflector, and the second reflector is a high-reflectivity reflector;
A configuration in which the first reflector is used as a base member, and the second reflector is pasted on the first reflector as a shape having the smallest area on the first shortest line and the largest area on the second shortest line; The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus.   The occupying area of the second reflector is gradually reduced from a large area portion on the second shortest line toward a small area portion on the first shortest line. 5. The image forming apparatus according to 4.   The image forming apparatus according to claim 1, wherein the photoconductor is a photoconductor using amorphous silicon.

Images