JP2007041140A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily obtain a more uniform and accurate electrification gap in a shaft direction in non-contact electrification for an image carrier performed by the electrification gap set by gap members on an electrifying roller. <P>SOLUTION: The pressing position of a photoreceptor 2 by a transfer roller 6a, that is, the arranging position of the transfer roller 6a relative to the photoreceptor 2 is set to an area δ on an opposite side to an area γ where the electrifying roller 3a is provided with respect to a line β passing through the center O of the photoreceptor 2 and orthogonal to a line α linking the center O of the photoreceptor 2 with the center A of the electrifying roller 3a. The width of the transfer roller 6a is set to be smaller than width between the gap members at both ends of the electrifying roller 3a. Thus, the deflection of the photoreceptor 2 by the pressing of the electrifying roller 3a is effectively restrained by the pressing of the transfer roller 6a so as to make the electrification gap constant in the shaft direction. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as an electrophotographic apparatus, an electrostatic copying machine, a printer, or a facsimile, and a ring-shaped gap member fixed to both ends of a charging roller provides a predetermined charging gap to an image carrier. The present invention relates to the technical field of an image forming apparatus which is set and non-contact charging the image carrier with this charging roller.

  2. Description of the Related Art Conventionally, as an image forming apparatus, an image forming apparatus including a charging roller that places a predetermined charging gap with respect to an image carrier and charges the image carrier in a non-contact manner is known (for example, see Patent Document 1). . As shown in FIG. 4, a charging roller a used in the image forming apparatus disclosed in Patent Document 1 is provided with a resistance layer c made of an elastic member having conductivity on the outer peripheral surface of a cored bar b. Insulating ring-shaped gap members d and e are fixed to the outer peripheral surfaces of both ends of c, respectively, and the pair of gap members d and e are in contact with the outer peripheral surface of the photosensitive drum f as an image carrier. By doing so, a predetermined charging gap G is set. In that case, although not specified in Patent Document 1, in general, the rotating shafts g and h projecting coaxially from the both end surfaces of the cored bar b in the axial direction are exposed by a biasing force of a spring (not shown). By pressing toward the body drum f, both gap members d and e are brought into pressure contact with the outer peripheral surface of the photosensitive drum f.

The charging roller a charges the photosensitive drum f in a non-contact manner by the charging gap, so that generation of ozone can be suppressed and foreign matters such as toner adhering to the photosensitive drum f are applied to the charging roller a. Since it is possible to prevent adhesion or substances contained in the resistance layer c of the charging roller a from adhering to the photosensitive drum f, the charging performance of the photosensitive drum f by the charging roller a can be improved.
JP 2004-109151 A.

  However, in the conventional image forming apparatus using the above-described charging roller a for non-contact charging, the gap members d, e between the pair of gap members d, e (in this specification, between the pair of gap members d, e). a structure in which the rotation shafts g and h positioned on the inner side of the e and the gap members d and e on the opposite side of the gap members d and e are pressed toward the photosensitive drum f by a spring. And that the rotation shafts i and j projecting coaxially from the both end surfaces of the photosensitive drum f in the axial direction are rotatably supported by a main body (not shown) via a bearing. When the drum f is pressed by the pair of gap members d and e, as shown in FIG. 4, the drum f bends (bends) in a direction away from the charging roller a. Usually, the deflection Do of the photosensitive drum f becomes maximum at the axial center point.

Further, the contact point of the gap members d and e with the photosensitive member f serves as a fulcrum, and the spring force urging portions of the rotary shafts g and h outside the gap members d and e serve as the force points, so that the pair of gap members The portion a ₁ of the charging roller a inside d and e bends (bends) Dr in a direction away from the photosensitive drum f, that is, in a direction opposite to the photosensitive member f. Usually, the deflection Dr of the charging roller a becomes maximum at the axial center point between the pair of gap members d and e.

  As described above, when the charging roller a and the photosensitive drum f bend in the opposite directions, the charging gap G between the charging roller a and the photosensitive drum f changes in the axial direction and is not constant. For this reason, charging of the photosensitive drum f by the charging roller a does not become uniform in the axial direction, and there is a problem that it is difficult to obtain stable and favorable charging.

  In particular, in recent years, electrophotographic image forming apparatuses such as electrophotographic printers have been increasingly required to be small and space-saving, so the internal process units and functional parts have been made smaller. It is necessary to construct them with high accuracy and to arrange them optimally. Therefore, the photosensitive drum and the charging roller are also required to be reduced in size. However, when the outer diameter or thickness of the photosensitive drum is reduced, or when the outer diameter of the charging roller is reduced, the above-described problems are caused. It is getting bigger.

  On the other hand, in the image forming apparatus described in Japanese Patent Application Laid-Open No. H10-228707, an area on the side opposite to the charging roller is exposed with respect to an orthogonal straight line that passes through the center of the photosensitive body and is orthogonal to a straight line that connects the center of the photosensitive body and the center of the charging roller. Since the transfer roller in contact with the body is provided, it is possible to slightly suppress the bending of the photoreceptor due to the pressing of the charging roller as described above.

  However, in the image forming apparatus described in Patent Document 1, since the transfer roller is simply disposed in the region opposite to the charging roller with respect to the orthogonal straight line, the photosensitive member is bent by the above-described pressing of the charging roller. It cannot be effectively suppressed. Therefore, in the image forming apparatus described in Patent Document 1, it is difficult to easily obtain a uniform and highly accurate charging gap in the axial direction.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an image carrier with a charging gap set by pressing gap members fixed to both ends of the charging roller against the image carrier. It is an object of the present invention to provide an image forming apparatus capable of performing stable and favorable charging by easily obtaining a uniform and highly accurate charging gap in the axial direction in the non-contact charging.

  In order to solve the above-described problems, an image forming apparatus according to the first aspect of the present invention includes an image carrier in which rotation shafts provided at both ends are rotatably supported by a main body through bearings, and both ends. An arrangement position of the charging roller on the opposite side with respect to a charging roller to which a gap member is fixed and an orthogonal straight line passing through the center of the image carrier and perpendicular to a straight line connecting the center of the image carrier and the center of the charging roller At least a pressing member that presses the image carrier, and the gap member is brought into pressure contact with the outer peripheral surface of the image carrier so that a charging gap is provided between the image carrier and the charging roller. In the image forming apparatus in which the charging roller non-contact charges the image carrier by the charging gap and presses the image carrier by the pressing member, the width of the pressing member is the charging It is characterized by being set smaller than the width between the gap member between the inner edges of the gap member in both end portions of the over la.

Further, in the image forming apparatus according to the second aspect of the present invention, the pressing member that presses the image carrier is an image forming component that makes contact with the image carrier and performs an image forming operation. The width of the member is set to be smaller than the width between the gap members.
Further, the image forming apparatus of the invention of claim 3 is a transfer roller in which the image forming component is in contact with the image carrier and transfers an image on the image carrier to a transfer medium, and the transfer roller Is set to be smaller than the width between the gap members.

  Further, the image forming apparatus of the invention of claim 4 includes a cleaning member that contacts the charging roller and cleans the charging roller, and the width of the cleaning member is larger than the width between the outer edges of the pair of gap members. The charging roller is set large, and the charging roller is pressed toward the image carrier by the cleaning member.

  According to the image forming apparatus of the present invention configured as described above, the charging roller is positioned with respect to an orthogonal straight line that passes through the center of the image carrier and is orthogonal to a straight line that connects the center of the image carrier and the center of the charging roller. Since the image carrier is pressed by the pressing member disposed on the opposite side, even if the image carrier is bent by the pressing of the charging roller, the deflection of the image carrier can be suppressed. As a result, the charging gap between the charging roller and the image carrier can be set to a constant value (50 μm) or less and substantially constant in the axial direction. Therefore, the charging of the image carrier by the charging roller can be made uniform in the axial direction, and a stable and stable long-term charging can be obtained.

  In particular, since the width of the pressing member is set smaller than the gap member width between the inner edges of the pair of gap members, the portion of the image carrier that faces the charging roller portion between the gap members, that is, image formation. It is possible to more reliably suppress the deflection of the charged region of the image carrier including the region. Therefore, the charging gap can be more effectively made substantially constant in the axial direction and set to a certain value (50 μm) or less.

  Further, since the charging gap can be made constant in the axial direction even when the image carrier is bent, the outer diameter of the charging roller can be reduced, and the outer diameter and thickness of the image carrier can be reduced. Therefore, as described above, it is possible to more effectively cope with the demands for downsizing and space saving which are increasingly demanded in recent years for image forming apparatuses.

  Furthermore, a special pressing member for pressing the image carrier can be eliminated by configuring the pressing member with an image forming component such as a transfer roller. Therefore, it is possible to prevent an increase in the number of parts while keeping the charging gap constant in the axial direction. As a result, it is possible to flexibly respond to demands for downsizing and space saving of the image forming apparatus.

  Further, since the pair of gap members and the portion of the charging roller between the gap members are pressed toward the image carrier by the cleaning member, the charging roller and the image carrier are forcibly bent in the same direction. be able to. As a result, the charging gap between the charging roller and the image carrier can be more effectively set to a constant value (50 μm) or less and constant in the axial direction. Therefore, the charging of the image carrier by the charging roller can be made even more uniform in the axial direction, and a more stable and favorable charging can be obtained in the long term. In particular, since each deflection of the charging roller and the image carrier can be maximized at the same position of the center point between the pair of gap members, the charging gap can be made constant with higher accuracy in the axial direction. It is possible to perform more stable and favorable charging.

  Further, the width of the cleaning member is set to be larger than the width between the outer edges of the pair of gap members, and the pair of gap members are pressed toward the image carrier by this cleaning member, so that they adhere to the surface of the gap member. Foreign matter such as toner can be effectively removed by the cleaning member. As a result, the charging gap G can be maintained at a constant value (50 μm) or less in the axial direction with high accuracy over a long period of time.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram schematically and partially showing an example of an embodiment of an image forming apparatus according to the present invention.

  As shown in FIG. 1, the image forming apparatus 1 of this example includes a photoconductor 2 that is an image carrier on which an electrostatic latent image and a toner image are formed, and the photoconductor 2 is provided around the photoconductor 2. Are sequentially provided with a charging device 3, an optical writing device 4, a developing device 5, a transfer device 6, and a cleaning device 7 from the upstream side in the rotation direction (clockwise in FIG. 1).

  In this example, the photosensitive member 2 is composed of a photosensitive drum, and a photosensitive layer having a predetermined thickness is formed on the outer peripheral surface of a cylindrical metal base tube in the same manner as a conventionally known photosensitive drum. A conductive tube such as aluminum is used for the metal base tube in the photoreceptor 2 and a conventionally known organic photoreceptor is used for the photosensitive layer. The photosensitive member 2 is provided such that rotary shafts 2a and 2b (shown in FIG. 2) that are coaxially provided in the axial direction from both end surfaces thereof are rotatably supported by a device body (not shown) via a bearing. ing.

  The charging device 3 has a non-contact charging roller 3a of this example and a cleaning member 3h made of, for example, a roller. The charging roller 3a uniformly charges the photoreceptor 2 in a non-contact manner, and the cleaning member 3h cleans the charging roller 3a to remove foreign matters such as toner and dust attached to the charging roller 3a.

  As shown in FIG. 2, the non-contact charging roller 3a includes a cored bar 3b. The cored bar 3b is configured as a conductive shaft having conductivity, such as a metal shaft. As this conductive shaft, for example, a SUM 22 surface with Ni plating can be used.

  The resistance layer 3c is formed on the outer peripheral surface of the cored bar 3b by applying a conductive coating material by, for example, spray coating. Gap members 3d and 3e made of a film member having a tape-like film thickness are fixed in a ring shape on the outer peripheral surfaces of both ends of the resistance layer 3c. The charging roller 3a includes rotating shafts 3f and 3g that are coaxially projected from both end surfaces of the cored bar 3b in the axial direction, and these rotating shafts 3f and 3g are rotatably supported by the apparatus body via bearings. Has been.

  The pair of gap members 3d and 3e are pressed against the outer peripheral surface of the photosensitive member 2 to set a predetermined charging gap G between the resistance layer 3c and the photosensitive member 2 based on a predetermined film thickness of the film member. In that case, a load by a spring (not shown) is applied to the bearing portions (not shown) of the rotating shafts 3f and 3g of the charging roller 3a as in the above-described conventional example, and the charging roller 3a is pressed in the direction of the photoreceptor 2. Thus, the gap members 3 d and 3 e are pressed against the outer peripheral surface of the photoreceptor 2.

The cleaning member 3h for cleaning the charging roller 3a is formed of a cylindrical sponge having a constant diameter. As the sponge of the cleaning member 3h, for example, a urethane sponge (trade name EPT-51, manufactured by Bridgestone Chemicals Tokyo) can be used. The sponge width (axial length) Lc of the cleaning member 3h is set to be larger than the width (axial distance) Lgo between the outer edges of the pair of gap members 3d, 3e (Lc> Lgo). The sponge of the cleaning member 3h includes a pair of gap members 3d, 3e and the photoreceptor 2 These gaps member 3d, these are in contact with the charging roller 3a part 3a ₁ of the inner 3e with a predetermined pressing force It is pushing toward.

  The optical writing device 4 writes an electrostatic latent image on the photosensitive member 2 with, for example, a laser beam. The developing device 5 includes a developing roller 5a, a toner supply roller 5b, and a toner layer thickness regulating member 5c. The toner T, which is a developer, is supplied onto the developing roller 5a by the toner supply roller 5b, and the toner T on the developing roller 5a is regulated in thickness by the toner layer thickness regulating member 5c. The electrostatic latent image on the photoconductor 2 is developed with the conveyed toner T, and a toner image is formed on the photoconductor 2.

The transfer device 6 has a transfer roller 6a for pressing the photoreceptor 2 with a predetermined pressing force, the width (axial length) L _T of the transfer roller 6a, a pair of gap members 3d, between the inner edges of the 3e It is set smaller than the width (axial distance) Lgi (L _T <Lgi). In this example, a transfer roller 6a that performs a transfer operation, which is an image forming operation, constitutes an image forming constituent member of the present invention and a pressing member of the present invention.

  The pressing position of the photoconductor 2 by the transfer roller 6a, that is, the position of the transfer roller 6a with respect to the photoconductor 2 passes through the center O of the photoconductor 2 and the center O of the photoconductor 2 and the center A of the charging roller 3a. An area δ opposite to the area γ where the charging roller 3a is provided with respect to the line β orthogonal to the connecting line α is set to an area δ where the toner image on the photoconductor 2 developed by the developing device 5 can be transferred. Yes. In this case, by appropriately setting the arrangement positions of the charging roller 3a, the developing device 5 and the transfer roller 6a, this region δ can effectively use the entire region opposite to the charging roller 3a with respect to the straight line β. .

By the transfer roller 6a, the toner image is transferred onto the photoreceptor 2 onto a transfer medium 8 such as transfer paper or an intermediate transfer medium. When the toner image is transferred to the transfer paper that is the transfer medium 8, the toner image on the transfer paper is fixed by a fixing device (not shown), an image is formed on the transfer paper, and the toner image is transferred to the transfer medium 8. When the toner image is transferred to the intermediate transfer medium, the toner image on the intermediate transfer medium is further transferred to the transfer paper, and then the toner image on the transfer paper is fixed by a fixing device (not shown) to form an image on the transfer paper. Is done.
In FIG. 2, the transfer medium 8 interposed between the photoreceptor 2 and the transfer roller 6a is not shown.

  The cleaning device 7 includes a cleaning member 7a such as a cleaning blade. The photosensitive member 2 is cleaned by the cleaning member 7a, and the transfer residual toner on the photosensitive member 2 is removed and collected.

  In the image forming apparatus 1 of this example configured as described above, since the transfer roller 6a is disposed in the above-described region δ, the charging roller 3a is photosensitive by the force with which the transfer roller 6a presses the photosensitive member 2. A force in a direction opposite to the force pressing the body 2 is generated, and the photosensitive member 2 is pressed by this force to bend toward the charging roller 3a. Therefore, when the charging roller 3a presses the photosensitive member 2 by the biasing force of the spring applied to the rotating shafts 3f and 3g of the charging roller 3a, the photosensitive member 2 is bent as shown in FIG. The photosensitive member 2 is bent toward the charging roller 3a by the above-described force based on the pressing force of the transfer roller 6a against the photosensitive member 2, so that the deflection Do of the photosensitive member 2 is suppressed.

In particular, the transfer width L _T of the roller 6a has a pair of gap members 3d, because it is smaller than the width Lgi (L _T <Lgi) set between the inner edges of 3e, a pair of gap members 3d, 3e between portion of the photosensitive member 2 opposed to the part 3a ₁ of the charge roller 3a is to be effectively pressed by the transfer roller 6a. Accordingly, it is possible to more reliably suppress the deflection Do of the photoconductor 2 that is maximum at the center point of the photoconductor 2.

As a result, the charging gap G between the charging roller 3a and the photoconductor 2 does not change greatly in the axial direction even if the photoconductor 2 is bent, and is set to be substantially constant and 50 μm or less in the axial direction. In particular, since the portion of the photosensitive member 2 that faces the portion 3a ₁ of the charging roller 3a between the gap members 3d and 3e is a charged region of the photosensitive member 2 including the image forming region, the charging gap G is more effective. Is substantially constant in the axial direction and is set to a certain value (50 μm) or less. Therefore, the charging of the photosensitive member 2 by the charging roller 3a becomes uniform in the axial direction, and stable and good charging is performed over a long period of time.

Further, a pair of gap members 3d, 3e and these gaps member 3d, the portion 3a ₁ of the charging roller 3a between 3e is pressed toward the photosensitive member 2 with a cleaning member 3h, the rotation shaft of the charging roller 3a Even if the charging roller 3a is pressed in the direction of the photoreceptor 2 by the biasing force of the spring applied to 3f and 3g, as shown in FIG. 2, the portion a ₁ of the charging roller a inside the pair of gap members 3d and 3e. Is bent in the direction approaching the photosensitive member 2, that is, in the same direction as the bending Do of the photosensitive member 2.

  As described above, when the charging roller 3a and the photosensitive member 2 are bent in the same direction, the charging gap G between the charging roller 3a and the photosensitive member 2 is not affected even if the charging roller 3a and the photosensitive member 2 are bent. It does not change greatly in the direction, and in combination with the above-described effect based on the pressing of the transfer roller 6a against the photosensitive member 2, it becomes constant with higher accuracy in the axial direction and is set more reliably at 50 μm or less. For this reason, the charging of the photosensitive member 2 by the charging roller 3a becomes more uniform in the axial direction, so that more stable and favorable charging is performed over a long period of time. In particular, since the deflections of the charging roller 3a and the photosensitive member 2 are maximum and almost parallel at the same position at the center point between the pair of gap members 3d and 3e, the charging gap G is more accurately in the axial direction. It becomes constant and further stable and good charging is performed.

  According to the image forming apparatus 1 of this example, since the photosensitive member 2 is pressed by the transfer roller 6a disposed in the region δ, the photosensitive member 2 is bent by the pressing of the photosensitive member 2 by the charging roller 3a. However, the deflection Do of the photoreceptor 2 can be suppressed. As a result, the charging gap G between the charging roller 3a and the photosensitive member 2 can be kept constant in the axial direction below a certain value (50 μm). Therefore, the charging of the photosensitive member 2 by the charging roller 3a can be made uniform in the axial direction, and good charging stable for a long time can be obtained.

In particular, the transfer width L _T of the roller 6a, a pair of gap members 3d, is made smaller than the width Lgi (L _T <Lgi) set between the inner edges of 3e, the charging roller 3a between gap member 3d, 3e portion of the photosensitive member 2 opposed to the part 3a _1, i.e. the deflection Do of the charged area of the photosensitive member 2 including the image forming region can be suppressed more reliably. Therefore, the charging gap G can be more effectively made substantially constant in the axial direction and set to a certain value (50 μm) or less.

  Further, since the photoconductor 2 is pressed by the transfer roller 6a so as to face the pressing direction of the photoconductor 2 by the charging roller 3a, a special pressing member for pressing the photoconductor 2 can be eliminated. Therefore, an increase in the number of parts can be prevented while keeping the charging gap G constant in the axial direction. As a result, it is possible to flexibly cope with the demand for downsizing and space saving of the image forming apparatus 1.

Further, a pair of gap members 3d, 3e and these gaps member 3d, since the pressing towards the photosensitive member 2 portions 3a ₁ of the charging roller 3a between 3e in the cleaning member 3h, the charging roller 3a and the photosensitive member 2 can be forced to bend in the same direction. As a result, the charging gap G between the charging roller 3a and the photosensitive member 2 can be more effectively reduced to a constant value (50 μm) or less and substantially constant in the axial direction. Therefore, the charging of the photosensitive member 2 by the charging roller 3a can be made even more uniform in the axial direction, and a more stable and favorable charging can be obtained in the long term. In particular, since each deflection of the charging roller 3a and the photosensitive member 2 can be maximized at the same central point between the pair of gap members 3d and 3e, the charging gap G can be made constant with higher accuracy in the axial direction. The body 2 can be more stably and satisfactorily charged.

  Further, the width Lc of the sponge of the cleaning member 3h is set larger than the width (axial distance) Lgo between the outer edges of the pair of gap members 3d and 3e (Lc> Lgo), and the pair of gap members is formed by the cleaning member 3h. Since 3d and 3e are pressed toward the photoreceptor 2, foreign matters such as toner adhering to the surface of the gap members 3d and 3e can be removed by the cleaning member 3h. As a result, the charging gap G can be maintained at a constant value (50 μm) or less in the axial direction with high accuracy over a long period of time.

  Further, since the charging gap G can be made constant in the axial direction even when the charging roller 3a and the photosensitive member 2 are bent, the outer diameter of the charging roller 3a can be reduced, and the outer diameter and thickness of the photosensitive member 2 can be reduced. Can be reduced. Therefore, as described above, it is possible to more effectively cope with the demands for downsizing and space saving which are increasingly demanded in recent years for image forming apparatuses.

  By the way, when non-contact charging is performed with the charging gap G set by the gap members 3d and 3e, the charging roller 3a is in contact with the photosensitive member 2 partially or entirely by compressing the gap members 3d and 3e. Even in such a case, the maximum value of the charging gap G in the axial direction is equal to or less than the film thickness of the gap members 3d and 3e (that is, 0 ≦ maximum value of the gap G ≦ film of the gap members 3d and 3e). (Thickness), there is no particular problem, and the desired effect of the present invention is achieved. Therefore, in the present invention, the non-contact charging performed in the charging gap G set by the gap members 3d and 3e includes such a case.

Next, an experiment conducted for demonstrating that the image forming apparatus of the present invention can obtain the above-described effects can be described with respect to an example belonging to the present invention and a comparative example not belonging to the present invention.
Table 1 shows the conditions of the photosensitive member 2, the conditions of the charging roller 3a, and the experimental results in the image forming apparatuses of Examples and Comparative Examples used in the experiment.

  In Table 1, each of the photoreceptors 2 used in Experiment Nos. 1 to 28 is used on the outer peripheral surface of an aluminum base tube as a photoreceptor layer of a photoreceptor LP-9000C manufactured by Seiko Epson Corporation. This is a photoreceptor in which the same organic photoreceptor as that described above is applied to a film thickness of 25 μm to form a photosensitive layer. In that case, the outer diameter of the photoreceptor 2 in Experiment Nos. 1 to 5 and 15 to 19 is φ40 mm, and the thickness of the aluminum base tube of the photoreceptor 2 of No. 1, 2, 15 and 16 is 1.5 mm. The thickness of the aluminum base tube of the photoreceptors 2 of No. 3 to 5 and 17 to 19 is 1.0 mm.

  The outer diameters of the photoreceptors 2 in Nos. 6 to 10 and 20 to 24 have a diameter of 30 mm, and the thickness of the aluminum tube of the photoreceptors 2 in Nos. 6, 7, 20, and 21 is 1.5 mm. Yes, the thickness of the aluminum base tube of the photoconductor 2 of No. 8 and 22 is 1.0 mm, and the thickness of the aluminum base tube of the photoconductor 2 of No. 9, 10, 23, and 24 is 0.75 mm. . Furthermore, the outer diameters of the photoreceptors 2 in Nos. 11 to 14 and 25 to 28 are 24 mm, and the thickness of the aluminum base tube of the photoreceptors 2 in Nos. 11, 12, 25, and 26 is 1.0 mm. No. 13, 14, 27, and 28, the thickness of the aluminum base tube of the photoreceptor 2 is 0.75 mm. Each photoconductor 2 was selected and used with a shake accuracy of 0.01 or less.

  The charging roller 3a used in each of Experiment Nos. 1 to 28 was processed into a shape that can be mounted on the above-described printer LP-9000C using a metal shaft having a SUM 22 plated with Ni as a core metal. These metal shafts are subjected to centerless polishing, and the runout accuracy is processed to 0.01 or less. As shown in Table 1, the metal shafts of Experiment Nos. 1, 4, 6, 10, 12, 15, 18, 20, 24, and 26 have an outer diameter of 12 mm, and Nos. 3, 8, 17, and No. 22, 5, 7, 9, 11, 13, 14, 16, 19, 21, 23, 25, 27, and No. 28 metal shafts have an outer diameter of φ10 mm. It is.

Then, conductive tin oxide (SnO ₂ ) and polyurethane (PU) resin are mixed at a weight ratio (wt ratio) of 1: 9 on the outer peripheral surfaces of these metal shafts, and dispersed in the ionic conductive material and water. The coating liquid obtained by spraying was spray-coated to form a resistance layer having a thickness of 20 μm. Conductive SnO ₂ is available from Gemco Co., Ltd. shown in Table 2. Details of those are available on Gemco's website (http://www.jemco-mmc.co.jp/corporate/index.html). It is posted.

The conductive SnO ₂ used in this example and this comparative example is trade name “T-1” of Gemco Co., Ltd., and “T-1” is a tin-antimony oxide. Of course, other conductive SnO ₂ can be used in the present invention. In addition, the ion conductive material is for imparting conductivity to the conductive coating material, and the ion conductive material used in this example and this comparative example is “YP-12” (manufactured by Maruhishi Oil Chemical Co., Ltd.). ). Incidentally, the above coating solution used in the experiment was coated in a thickness of 20μm aluminum plate, was measured for volume resistivity was (1.0~5.0) × ¹⁰ 10 Ωcm.
The gap members 3d and 3e were formed by affixing a polyimide (PI) resin tape having a film thickness of 20 μm and a width of 5 mm to the outer peripheral surfaces of both ends of the charging roller 3a.

  In the pressing method, the charging roller 3a was pressed by applying a spring load to the bearing portions (positions 10 mm from the outer edges of the gap members 3d and 3e) of the rotating shafts 3i and 3j of the charging roller. The bearing spring load in that case is 200 gf in No. 1, 2, 5, 8, 10, 13, 15, 16, 19, 22, 24, and 27, and No. 3, 6, 7, 11, 17 20, 21, and 25 are 500 gf, and Nos. 4, 9, 12, 14, 18, 23, 26, and 28 are 800 gf.

  As the experimental apparatus for the image forming apparatus, a printer in which the above-described printer LP-9000C was partially modified so that this experiment can be performed was used. In this case, since the printer LP-9000C uses a photoreceptor having an outer diameter of φ40 mm, when performing an experiment using a photoreceptor having an outer diameter other than φ40 mm, the scale is the same as that of the printer LP-9000C. The image forming apparatuses with different image quality were prepared, and an image forming experiment was performed using the same engine as the printer LP-9000C.

Further, in this experimental apparatus, as shown in FIG. 3, the cleaning device 7 for the photosensitive member 2 and the cleaning member 3h for the charging roller 3a shown in FIG. By omitting the cleaning device 7 for the photoconductor 2, the pressing position of the photoconductor 2 by the transfer roller 6a, that is, the arrangement position of the transfer roller 6a can be flexibly changed. Then, the correlation position of the center O of the photosensitive member 2, the center A of the charging roller 3a, and the center B of the transfer roller 6a, that is, the arrangement position of the transfer roller 6a, is the rotation direction of the photosensitive member 2 (see FIG. An experiment was conducted by changing the position of the transfer roller 6a by changing the angle AOB formed in a clockwise direction in the example. In addition, the position of the charging roller 3a is fixed, and the position of the developing device 5 is appropriately changed according to the arrangement position of the transfer roller 6a.
Even if the cleaning device 7 and the cleaning member 3h are omitted, pressing the photosensitive member 2 toward the charging roller 3a with the transfer roller 6a does not affect the present invention.

  The transfer conditions are as follows. That is, as shown in Table 1, the angle ∠AOB indicating the arrangement position of the transfer roller 6a is 160 ° in Experiment Nos. 1, 8, 12, 15, 22, and 26, and Nos. 2, 7, 13 16, 21, and 27 are 180 °, Nos. 3, 6, 9, 17, 20, and 23 are 240 °, and Nos. 4, 10, 18, and 24 are 270 °. .5, 11, 14, 19, 25, and 28 are 280 °. The pressing force of the photosensitive member 2 by the transfer roller 6a is 500 gf in No. 1, 4, 5, 9, 11, 13, 14, 15, 18, 19, 23, 25, 27, and 28. 2, 3, 6, 8, 10, 12, 16, 17, 20, 22, 24, and 26 are 800 gf and No. 7 and 21 are 1000 gf.

The width (transfer width) of the transfer roller 6a is the same (smaller) than the width between the inner edges of the gap members 3d and 3e in Experiments Nos. 1 to 14, and the gaps in Nos. 15 to 28. The width (large) is larger than the width between the inner edges of the members 3d and 3e.
As is clear from the above, Experiment Nos. 1 to 3, 6 to 9, 12, and 13 are examples of the present invention, and Nos. 4, 5, 10, 11, 14, and 15 to 28 are examples. It is a comparative example of the present invention.

In performing the image formation experiment, the peripheral speed of the photosensitive member 2 was set to about 210 mm / sec in all the experiments. The applied voltage V _C (V) of the charging roller 3a is obtained by superimposing the _AC voltage AC component V _AC (V) on the DC voltage DC component V _DC (V) in any experiment,
V _C = V _DC + V _AC = −650 + (1/2) V _PP · sin2πft
(Here, V _PP = 1750 V, f = 1.3 kHz, and V _AC is a sin wave.)
Set to. In the experiment, 500 sheets of 5% halftone monochrome printing were continuously performed on A3 plain paper in an indoor environment at a temperature of 23 ° C. and a humidity of 50%.

  Then, the 100th, 200th, 300th, 400th, and 500th printed matters are picked up and judged by visual observation. Only when there are no image spots on these printed matters, the printed matter is judged to be extremely good. In Table 1, circles indicate that there is no image unevenness up to the 300th sheet, but good charging is observed. In this case, it is judged that it is not good in the present invention and is represented by Δ in Table 1. If any one of these printed matter has image spots, it is judged that charging is defective and Table 1 shows x. expressed.

  In the image forming apparatuses of Examples Nos. 1 to 3, 6 to 9, 12, and 13, all were excellent and good charging was obtained. Moreover, in each comparative example of experiment No. 15-17, 20-23, 26, and 27, all looked like an image spot, and although it is unsatisfactory as this invention, it is a grade which can be put to practical use by (triangle | delta). Charge was obtained. Further, in each of the comparative examples of Experiment Nos. 4, 5, 10, 11, 14, 18, 19, 24, 25, and 28, image spots were observed, and the result of poor charging of x was obtained.

  According to this experiment, in the non-contact charging of the photosensitive member 2 by the charging roller 3, the above-described operational effects of the present invention can be obtained by pressing the photosensitive member 2 by the transfer roller 6a disposed in the region δ. Proven. That is, it was confirmed that not only the transfer roller is provided in the region δ but also that the transfer roller 6a is set to have a width smaller than the width between the inner edges of the pair of gap members 3d and 3e, so that extremely good charging can be obtained. .

  The image forming apparatus of the present invention is an image forming apparatus such as an electrophotography, an electrostatic copying machine, a printer, a facsimile, or the like. By setting a predetermined charging gap with respect to the body, it can be suitably used in an image forming apparatus in which the photoreceptor is non-contact charged by a charging roller.

1 is a diagram schematically and partially showing an example of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a diagram schematically illustrating a photoconductor, a charging roller, a charging roller cleaning member, and a transfer roller used in the image forming apparatus illustrated in FIG. 1. It is a figure which shows typically the image forming apparatus used with the experimental apparatus. It is a figure which shows typically the behavior of the photoconductor and the charging roller in the conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Photoconductor, 3 ... Charging device, 3a ... Charging roller, 3c ... Resistance layer, 3d, 3e ... Gap member, 6 ... Transfer device, 6a ... Transfer roller

Claims (4)

An image carrier in which rotation shafts provided at both ends are rotatably supported by the apparatus main body via a bearing, a charging roller having gap members fixed to both ends, and a center of the image carrier and A pressing member that presses the image carrier by disposing the charging roller on the opposite side with respect to an orthogonal straight line orthogonal to a straight line connecting the center of the image carrier and the center of the charging roller, When the gap member is pressed against the outer peripheral surface of the image carrier, a charging gap is set between the image carrier and the charging roller, and the charging roller non-contact charges the image carrier by the charging gap. And an image forming apparatus that presses the image carrier with the pressing member.
2. The image forming apparatus according to claim 1, wherein the width of the pressing member is set to be smaller than the width between the gap members between the inner edges of the gap member at both ends of the charging roller. The pressing member that presses the image carrier is an image forming component that contacts the image carrier and performs an image forming operation.
2. The image forming apparatus according to claim 1, wherein a width of the image forming component member is set smaller than a width between the gap members. The image forming component member is a transfer roller that contacts the image carrier and transfers an image on the image carrier to a transfer medium,
The image forming apparatus according to claim 2, wherein a width of the transfer roller is set to be smaller than a width between the gap members. A cleaning member that contacts the charging roller and cleans the charging roller;
The width of the cleaning member is set larger than the width between the outer edges of the pair of gap members, and the charging roller is pressed toward the image carrier by the cleaning member. The image forming apparatus according to any one of 1 to 3.

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