JP6292889B2 - A charging member, a process cartridge, and an image forming apparatus. - Google Patents

Description

  The present invention relates to a contact-type charging device that makes a charging member come into contact with a member to be charged such as a photosensitive member to charge / discharge the surface of the member to be charged, an image forming apparatus including the charging device, and a detachable attachment to the image forming apparatus. It relates to a process cartridge.

  An electrophotographic image forming apparatus such as a copying machine or a laser beam printer forms an electrostatic latent image by irradiating a uniformly charged electrophotographic photosensitive member with light corresponding to image data. Then, a developer (toner) that is a recording material is supplied from the developing device to the electrostatic latent image to be visualized as a toner image. The toner image is transferred from the photosensitive member to a recording material such as a recording sheet by a transfer device, and fixed on the recording material by a fixing device to form a recorded image. The surface of the photoreceptor after separation of the recording material is cleaned by scraping off the transfer residual toner by a cleaning device, and is repeatedly used for image formation.

  As a method for charging the surface of the photosensitive member, a charging member is brought into contact with the surface of the photosensitive member as a member to be charged and a voltage is applied to the charging member from the viewpoint of a low voltage process, a low ozone generation amount, and a low cost. There is contact charging that charges the surface of the photoreceptor.

  The voltage applied to the charging member includes a method in which only a DC voltage is applied (DC application method) and a method in which an alternating voltage whose voltage value changes periodically with time (AC application method) is applied. The AC application method has an advantage that the latitude of uniform charging is larger than that of the DC application method.

  As described above, when the vibration voltage is applied to the charging member by the AC application method, unevenness corresponding to the cycle of the AC voltage component occurs in the charging potential. Then, when the scanning exposure image frequency on the photosensitive member and the spatial frequency of the above-described charging unevenness are close to each other, a beat is generated on the image due to the interference between both, and the image is observed as a moire pattern of image density. That is, it is considered that the final surface potential of the photosensitive member is determined at the last moment when the charging member and the photosensitive member are separated. For this reason, if the discharge nip exit is a straight line, the charging unevenness on the surface of the photoreceptor based on the AC component also becomes a straight line, so that it is easy to cause interference when the image frequency of the horizontal line approaches the spatial frequency of the charging unevenness, Moire is noticeable.

  Therefore, in Patent Document 1, a sponge surface layer is provided on the contact charging member, and irregularities formed by sponge cells are randomly arranged. With this configuration, the discharge nip does not become a complete straight line, so the variation in charging potential that occurs on the surface of the charged object according to the frequency of the AC component does not become linear, and it becomes difficult to interfere with the scanning exposure image frequency, resulting in the generation of moiré. Suppressed.

Japanese Patent Application No. 4-18324

  However, in Patent Document 1, the sponge cells constituting the charging member surface have irregularities. For this reason, with the use of the cartridge, the toner developer and the external additive that have not been cleaned by the cleaning blade may be collected by the uneven portions on the surface of the charging member. In other words, fine powder or coarse powder of developer or fine powder such as an external additive used for the developer accumulates in the irregularities of the cells. Then, the charging member loses a space (gap) necessary for discharge at the contact nip with the photosensitive member (photosensitive drum). As a result, discharge becomes difficult in the contact nip. For this reason, the discharge is performed in a narrow area outside the contact nip (an area extending linearly in the longitudinal direction of the charging member). Therefore, charging unevenness corresponding to the AC component of the alternating current applied to the charging member occurs on the photosensitive drum. If the charging unevenness generated on the photosensitive drum interferes with the scanning exposure image frequency, moire may occur in the image formed on the photosensitive member.

  Further, the external additive is stored in the unevenness of the sponge constituting the charging member, so that the photosensitive drum is mechanically rubbed. As a result, there is a possibility that the photosensitive drum is scratched and a cleaning failure occurs.

  In particular, when the penetration amount to the photosensitive drum is set to be the same in the longitudinal direction of the cleaning blade, the central portion of the photosensitive drum is warped by the supported end because the photosensitive drum is pressed by the cleaning blade. End up. The contact pressure is higher at the end than at the longitudinal center. Accordingly, since the rubbing force of the cleaning blade is larger than that at the center, the surface of the photosensitive drum surface layer is easily scraped from the center.

  Further, the surface layer of the photosensitive drum is worn due to rubbing when the recording material passes through the transfer nip portion between the photosensitive drum and the transfer roller. Further, the transfer pressure at the transfer nip portion between the photosensitive drum and the transfer roller with the recording material interposed therebetween is higher at the end portion of the recording material than at the central portion in the longitudinal direction. Accordingly, the amount of paper edge (paper dust) generated at the end of the recording material increases. This paper edge (paper dust) may accumulate in the cleaning blade nip and damage the photosensitive drum. Accordingly, the surface layer of the photosensitive drum is easily worn at the end of the recording material where a large amount of paper edge (paper dust) is generated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a charging member that reduces the abrasion of the photosensitive member while suppressing the occurrence of moire.

In order to achieve this object, the charging member of the present invention is disposed along the longitudinal direction of the image carrier of the image forming apparatus, and is a charging member that charges the image carrier. One surface region and two second surface regions, and the first surface region is disposed between the two second surface regions with respect to the longitudinal direction, and the first surface region The surface is rough enough to form a gap that enables discharge between the image carrier and the charging member on the contact surface with the image carrier when the charging member contacts the image carrier. Yes, the surface of the second surface region can be discharged between the image carrier and the charging member at a contact surface with the image carrier when the charging member contacts the image carrier. to form a gap, said first surface area of the roughness low roughness Sadea than The image bearing member, and a said longitudinal outer non-image forming area of the image forming region and the image forming region on the surface, the respect to the longitudinal direction, the second surface and the first surface region The position of the boundary with the region is in the vicinity of the position of the boundary between the image forming region and the non-image forming region, and the second surface region is closer to the image carrier than the first surface region. The amount of discharge is small.

  The charging member of the present invention has a first surface region having a roughness that can be sufficiently discharged when it contacts the image carrier, and the first surface region so that the amount of discharge is less than that of the first surface region. The second surface region has a roughness lower than the roughness. The first surface area corresponds to the image forming area in the longitudinal direction, and the second surface area corresponds to the non-image forming area in the longitudinal direction. For this reason, the non-image forming area of the image carrier without toner is easily worn, but the discharge amount is small in the second surface area of the charging member, so that the wear of the image carrier can be prevented.

1 is a schematic cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a cross-sectional view of the charging roller of the embodiment of the present invention. It is a graph which shows the roughness in the middle of the longitudinal direction of the charging roller according to the embodiment of the present invention. It is a schematic diagram which shows the mode of 10 division | segmentation of the longitudinal direction of the charging roller of embodiment of this invention. In the embodiment of the present invention, it is a diagram showing a state of measurement of the air gap between the photosensitive drum and the charging roller. 6 is a graph illustrating an example of a result of measuring an air gap between a photosensitive drum and a charging roller in the embodiment of the present invention. FIG. 4 is an enlarged schematic diagram of a contact portion between a charging roller and a photosensitive drum in the embodiment of the present invention. FIG. 7A shows a state in which the charging roller is not pressed, and FIG. 7B shows a state in which the charging roller is pressed against the photosensitive drum by the pressure, and the distance between the photosensitive drum and the charging roller. Indicates a compressed state. It is a table | surface which shows the measurement result of an air gap, and the result of the air gap by calculation for every division | segmentation of the longitudinal position shown in FIG. In another embodiment of the present invention, the length of the charging roller is divided into 10 and is a graph showing the roughness therebetween. FIG. 10 is a schematic diagram showing 10 divisions in the longitudinal direction of the charging roller shown in FIG. 9.

  Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. However, the relative arrangement of components, the display screen, and the like described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified.

  In the present specification, the terms representing the directions such as up, down, right, and left in the configuration and operation of the image forming apparatus indicate directions in the normal use state unless otherwise specified. That is, the normal use state of the image forming apparatus is a state in which the image forming apparatus is properly attached to the properly arranged image forming apparatus and can be used for an image forming operation.

<First Embodiment>
(Overall configuration of image forming apparatus)
An image forming apparatus according to an embodiment of the present invention will be described.

  FIG. 1 is a schematic cross-sectional view illustrating a schematic configuration of an image forming apparatus according to the present embodiment.

  The image forming apparatus 100 includes the following elements. The photosensitive drum 1 (image carrier) carries a developer image and is rotatably provided. The charging roller 2 has a roller shape, and performs a charging process on the surface of the photosensitive drum 1 before forming a latent image. The exposure device 3 performs an exposure process on a charged part on the surface of the photosensitive drum 1 to form a latent image.

  The developing device 10 converts the latent image formed and supported on the surface of the photosensitive drum 1 into a visible image using a developer. The transfer roller 20 transfers a visible image formed and supported on the surface of the photosensitive drum 1 to a sheet-like recording medium K and forms an unfixed image on the recording medium K. The fixing device 30 performs a fixing process on the recording medium K carrying an unfixed image, and fixes and records the unfixed image on the recording medium K. The cleaning device 40 removes and collects the residue on the surface of the photosensitive drum 1 after the transfer process and prepares for the next latent image formation.

  Note that the photosensitive drum 1, the charging roller, the developing device 10, and the cleaning device 40 integrally form a process cartridge and are detachable from the main body of the image forming apparatus.

  In FIG. 1, a recording medium K is conveyed in the direction of arrow A, and is discharged outside the image forming apparatus 100 after transfer processing and fixing processing. In this embodiment, as the developer, a one-component magnetic developer composed of a styrene acrylic resin and a magnetic material having an average particle diameter = 7 μm and an average circularity of 95 is employed.

  Next, the image forming process according to the present embodiment will be described with reference to FIG.

  In the image forming apparatus 100, the photosensitive drum 1 is rotationally driven at a predetermined process speed (200 mm / Sec). The charging roller 2 holds both ends of the cored bar rotatably by bearing members (not shown), and is urged toward the photosensitive drum 1 by a pressure spring (not shown). Is pressed with a predetermined pressing force (500 g weight). The charging roller 2 rotates following the rotation of the photosensitive drum 1.

  A predetermined charging bias is applied from the high-voltage power supply 50 to the charging roller 2 via the metal core, whereby the peripheral surface of the rotating photosensitive drum 1 is charged to a predetermined potential. In the present embodiment, the applied bias is a superimposed oscillating voltage of a sine wave of Vdc = −550V, Vpp = 1400V, and f = 1400 Hz.

  Further, by exposing the charged portion on the surface of the photosensitive drum 1 with a laser from the exposure device 3, a latent image having a photosensitive potential Vl = −130 V is formed on the charged portion on the surface of the photosensitive drum 1. It is formed.

  The latent image formed and supported on the surface of the photosensitive drum 1 is a visible image, and the visible image formed and supported on the surface of the photosensitive drum 1 is a recording medium that reaches between the photosensitive drum 1 and the transfer roller 20. The image is transferred to K and an unfixed image is formed on the recording medium K.

  The photosensitive drum 1 is a reversal developing type photosensitive drum in which an OPC layer having a diameter of 24 mm and an aluminum cylinder is coated on an aluminum cylinder, and the outermost layer is constituted by a charge transport layer using a modified polycarbonate as a binder resin. .

  In this way, the recording medium K carrying the unfixed image is subjected to the fixing process from the fixing device 30, the unfixed image is fixed and recorded on the recording medium K, and the recording medium K after the fixing process is external to the image forming apparatus 100. As a result, the series of image printing processes is completed.

  The residue on the surface of the photosensitive drum 1 after the transfer process is removed and collected by the cleaning device 40, whereby the photosensitive drum 1 is prepared for the next latent image formation.

  Next, the charging member of this embodiment will be described in detail.

(Layer structure of charging roller)
The layer configuration of the charging member according to this embodiment will be described.

  FIG. 2 is a cross-sectional view of the charging roller 2.

  As shown in the figure, the charging roller 2 includes a cylindrical conductive support 2a, a conductive elastic layer 2b (elastic layer) formed on the outer periphery thereof, and a surface covering the outer periphery of the conductive elastic layer 2b. A layer 2c (elastic layer). A plurality of minute protrusions are provided on the surface of the surface layer 2c.

  The conductive elastic layer 2b was formed by mixing a conductive agent and a polymer elastic body into a roller shape concentrically and integrally on the outer periphery of the conductive support 2a. As the conductive agent, for example, an ionic conductive agent such as a quaternary ammonium salt or an electronic conductive agent such as carbon black is used. As the polymer elastic body, for example, epichlorohydrin rubber or acrylonitrile rubber is used.

  Thereafter, the thickness of the conductive elastic layer 2b is adjusted by polishing to obtain a crown shape of 10 to 200 μm. In this embodiment, the crown amount is 100 μm. Furthermore, after producing the conductive elastic layer 2b, a surface layer 2c is provided as a covering layer.

  The surface layer 2c contains at least a surface layer binder and fine particles (volume average particle diameter of 10 to 50 μm, preferably 20 to 40 μm) as a surface roughening agent, and the fine particles may be either spherical particles or irregular particles. Further, the amount of fine particles with respect to the surface layer binder is 10 to 100 wt%.

  Subsequently, various physical property values of the charging member in the present embodiment will be described.

(Charge roller hardness)
The Asker C hardness of the charging roller 2 is preferably 50 ° to 85 °. In this embodiment, the Asker C hardness of the charging roller 2 is 85 °.

  The Asker C hardness was measured by measuring the ASKER C constant load measurement at 9.8 N (1.0 Kgf) at the central portion of the roller surface and the circumferential 120 ° pitch positions on the both sides 90 mm from the central portion (9 locations in total). Measured with

  The MD-1 hardness of the charging roller 2 was 60 to 85 degrees, preferably 60 to 70 degrees. In the present embodiment, the Asker C hardness of the charging roller 2 is 64 degrees.

  The Asker C hardness is measured by leaving the roller in 23 ° C./53 RH for 4 hours or longer, and then setting the 180 ° pitch position in the circumferential direction of the roller surface center and 90 mm on both sides from the center (total of 6 positions). It is the measurement average value measured with the MD-1 micro rubber hardness meter.

(Young's modulus of charging roller)
In this embodiment, when the Young's modulus of the combined layer of the conductive elastic layer 2b and the surface layer 2c of the charging roller 2 is defined as the synthetic Young's modulus, the synthetic Young's modulus is preferably 10 to 200 MPa, and particularly preferably 50 to 150 MPa. It is. Incidentally, synthetic Young's modulus of the charging roller 2 under a load of 100 mN / mm ² at 1 minute by the universal hardness meter (Fischer Corp. surface film physical property tester Fischer Scope H100C), load is reached 100 mN / mm ² The synthetic Young's modulus was calculated from the later strain amount. The synthetic Young's modulus of the charging roller 2 used in this embodiment was 64 MPa.

(Charging roller resistance)
The resistance value of the charging roller 2 is 1.0 × 10 ⁷ Ω · cm at 23 ° C. and 53% RH.
-1.0 * 10 < ⁹ > ohm * cm is preferable. The resistance value of the present embodiment was 5.0 × 10 ⁷ Ω · cm. The measured value was measured as follows. After leaving the charging roller 2 in 23 ° C. and 53% RH for 24 hours or more, measure the total load on the Φ30 mirror metal roller of the current measuring device in that environment 9.8 N (1.0 kgf) (end load 4.9 N) (0.5 kgf) × 2). The measured value is a value when a DC 200 V voltage is applied while the Φ30 mirror surface metal roller is driven to rotate at a speed of 30 rpm.

(Method for manufacturing charging roller)
Next, a method for manufacturing the charging roller 2 in the present embodiment will be described. A surface layer solution having a particle size of 1 to 8 μm is applied on the base layer. After that, only the longitudinal and non-image areas of the charging roller 2 are masked. Thereafter, a surface layer liquid having a particle diameter of 10 to 40 μm is applied to an image area that has not been subjected to masking. In this manner, the transition point of roughness is provided by performing the masking process.

  As a manufacturing method, the following manufacturing method can be used in addition to the masking process as in the present embodiment.

  That is, in the case where the surface is formed by spraying particles onto the surface of the charging roller 2 by an apparatus, particles having a large roughness are sprayed on the image forming area, and particles having a small roughness are sprayed on the non-image area. It is also possible to change the longitudinal surface roughness by spraying.

  It is also possible to change the longitudinal surface roughness by wiping the surface layer agent in the non-image area after coating the surface layer.

  In any case, it is sufficient that a transition point of the surface roughness can be provided in the longitudinal direction of the charging roller 2.

(Charge roller surface roughness)
Fine particle toner functions as a lubricant on the cleaning blade that contacts the image forming area of the photosensitive drum 1. However, since no toner is present in the non-image forming area of the photosensitive drum 1, the friction coefficient between the photosensitive drum 1 and the cleaning blade is increased in the non-image forming area. Therefore, the non-image forming area tends to advance the abrasion of the photosensitive drum 1 faster than the image forming area. For this reason, when the amount of scraping at the end of the image area of the photosensitive drum 1 is increased, severe vertical stripes may occur on the image or in the sheet passing portion (blank portion) outside the image.

  In this embodiment, focusing on this point, a transition point of roughness is provided at the end of the image forming area, and the amount of discharge is reduced in the non-image area, thereby suppressing the amount of scraping of the drum and abnormal images such as vertical stripes. It suppresses generation | occurrence | production of this.

  The ten-point average roughness of the surface of the charging roller 2 in the image area in the present embodiment is Rzjis = 15 to 50 μm, preferably Rzjis = 20 to 30 μm. In the present embodiment, the surface of the charging roller 2 is Rz = 26 μm.

  Further, the ten-point average roughness of the surface of the charging roller 2 in the non-image area in the present embodiment is preferably Rzjis = 0.1 to 15 μm. In the present embodiment, a charging roller having an average roughness of the non-image area of Rz = 2.6 μm is used.

  In the present embodiment, Rzjis measurement is based on JIS-B0601-2001. And using a surface roughness measuring device Surfcorder SE3500 type manufactured by Kosaka Laboratory Ltd., in the longitudinal direction, the measurement length is 8.0 mm, the cutoff value is 0.8 mm, and the measurement speed is 0.3 mm / sec. It was measured.

  FIG. 3 is a graph showing the roughness of the charging roller 2 divided into 10 in the longitudinal direction. FIG. 4 is a schematic diagram showing a state in which the charging roller 2 is divided into 10 in the longitudinal direction.

  As shown in these drawings, for the sections 3 to 8 (first surface region), the ten-point average roughness Rzjis (μm) of the surface satisfies 15 ≦ Rzjis ≦ 50. The ten-point average roughness Rzjis (μm) of the surface was 21 μm.

  Further, in the sections 1 to 2 and the sections 9 to 10 (second surface region), the ten-point average roughness Rzjis (μm) of the surface satisfies 15> Rzjis.

  Thus, the charging roller 2 has the first surface region (sections 3 to 8) and the second surface region (sections 1 to 2 and sections 9 to 10) outside the first surface region in the longitudinal direction. Further, the longitudinal position of the boundary between the first surface area and the second surface area is in the vicinity of the longitudinal position of the boundary between the image forming area and the non-image forming area of the photosensitive drum 1.

  In this embodiment, the average of section 1 to section 2 was 6.3 μm, and that of sections 9 to 10 was 6.1 μm.

  That is, when the Asker C hardness of the charging roller 2 is not less than 50 ° and not more than 85 °, sections 10 to 8 where the ten-point average roughness Rzjis (μm) of the surface of the charging roller 2 satisfies 15 ≦ Rzjis ≦ 50. In the (first surface region), since the surface is rough, sufficient discharge is possible. On the other hand, when the Asker C hardness of the charging roller 2 is 50 ° or more and 85 ° or less, in the second surface region where the ten-point average roughness Rzjis (μm) of the surface of the charging roller 2 satisfies 15> Rzjis. The amount of discharge is less than that of the first surface region. It should be noted that the phrase “the amount of discharge is small” includes the case where no discharge occurs.

  Next, the discharge at the contact portion between the charging roller 2 and the photosensitive drum 1 in the image forming area and the non-image forming area in the present embodiment will be described.

(Discharge gap calculation)
A voltage applied between the charging roller 2 and the conductive base layer of the photosensitive drum 1 as a member to be charged is formed between the electrostatic capacitance C1 of the photosensitive layer and the charging roller 2 and the photosensitive layer. This is distributed to the capacitance C2 of the small air gap G. The photoreceptor layer is an OPC photoreceptor layer having a relative dielectric constant of 3 and a thickness of 18 μm. Specifically, the electrostatic capacity C1 of the photoreceptor layer and the electrostatic capacity C2 of the air layer are expressed as follows, where d is the thickness of the air layer and the unit is μm.
C1 = 3 × 8.85 × 10 ⁻¹² × 1/18 × 10 ⁻⁶
C2 = 1 × 8.85 × 10 ⁻¹² × 1 / d × 10 ⁻⁶
It is expressed as

On the other hand, the dielectric breakdown voltage Vz of the minute air layer is Vz = 312 + 6.2d (7.7 × 10 ⁻⁶ m <d) based on Paschen's law at atmospheric pressure.
And given.

Also, under atmospheric pressure, when the thickness of the air layer becomes 7.7 μm or less, discharge is not performed according to Paschen's law. Therefore, when the applied voltage is V [V], the voltage Vair actually applied to the air layer is ,
When Vair = C1 / (C1 + C2) × V, and Vair ≧ Vz, discharge is performed. Therefore, when 1000 V is applied, the interval distance d of the dischargeable air gap G is d = 7.7 to 102 μm, and when 2000 V is applied, the interval distance d of the dischargeable air gap G is d = 7. .7 to 265 μm.

  Based on the gap calculation described above, the charging roller 2 of the present embodiment examines the correlation with the gap formed when contacting the photosensitive drum 1.

(Gap measurement at contact part)
On the contact surface between the photosensitive drum 1 and the charging roller 2 in the charging roller 2, the gap height (hereinafter referred to as air gap G) that can be formed between the photosensitive drum 1 and the charging roller 2 was measured.

  As a measuring method, a gap measuring machine GM1000L (manufactured by Optron) was used.

  FIG. 5 is a diagram showing how the air gap G between the photosensitive drum 1 and the charging roller 2 is measured.

  In the measurement, after leaving the charging roller at 23 ° C. and 53% RH for 2 hours or more, as shown in FIG. 5, the charging roller is brought into contact with a 基準 50 matte reference metal roll 110 with a load of 9.8 N (1 kg weight). It was. Then, with the matte reference metal roll 110 rotated at 0.32 rps, a laser scan 112 was performed from the back, and the gap generated between the charging roller 2 and the reference metal roll 110 was measured with the laser light receiving device 111 for 3 seconds. .

  FIG. 6 is a graph showing an example of the result of measuring the air gap G between the photosensitive drum 1 and the charging roller 2.

  The range of the gap height in the image forming area of the charging roller 2 is preferably 5 to 30 μm, and the charging roller 2 of the present embodiment has an average of 16 μm. On the other hand, the gap height in the non-image area is preferably 0 to 15 μm, and the charging roller 2 of the present embodiment has an average of 3 μm.

  As described above, from the gap measurement result at the contact portion and the discharge gap calculation result, the charging roller 2 does not discharge in the longitudinal direction of one charging roller and the discharge area between the photosensitive drum 1 and the charging roller. It is characterized by a mixture of areas.

In other words, the air gap G between the photosensitive drum 1 and the charging roller 2 in the image forming area exceeds the dischargeable distance 7.7 × 10 ⁻⁶ m calculated by Paschen's law. The height of the gap (air gap G) between the photosensitive drum and the charging member in the non-image area is characterized by not exceeding the dischargeable distance 7.7 × 10 ⁻⁶ m calculated by Paschen's law. .

  Next, the theoretical calculation using the physical properties of the charging roller 2 for the air gap G will be described.

  FIG. 7 is an enlarged schematic view of a contact portion between the charging roller 2 and the photosensitive drum 1. FIG. 7A shows a state in which the charging roller 2 is in contact with no pressure, and FIG. 7B shows that the charging roller is pressed against the photosensitive drum 1 by the applied pressure P and charged with the photosensitive drum 1. It is a figure which shows the state by which the distance with the roller 2 was compressed. At this time, if the minute protrusion α is not deformed due to high hardness particles, when the distance between the photoconductor drum and the charging member is compressed, the protrusion is surfaced due to the rubber characteristic of the surface layer 2 c of the charging roller 2. It can be assumed that it is embedded in the layer 2c.

  In FIG. 7A, the height of the minute protrusion α formed on the surface layer 2c by the surface roughening agent or fine particles by foaming is L [m]. From this state, as shown in FIG. 7B, when the pressure P [N] is applied to the charging roller 2 and the minute protrusion α is elastically deformed and pushed into the surface layer 2c, the deformation of the charging roller 2 is deformed. Let the amount be X [m]. At this time, a gap formed between the surface layer 2c of the charging roller 2 and the photosensitive drum 1, an air gap G [μm], is expressed by Expression (1).

G = L−X (1)
At this time, assuming that the rubber is a spring and the distortion coefficient is Y, the deformation amount of X is calculated from the Hooke's law:
X = YL (2)
It can be expressed. The distortion coefficient Y is a composite Young's modulus E [MPa] of the charging roller 2;
Assuming that the stress received by the microprojection α is Z [N / m], from the Hooke's law,
Y = Z / E (3)
It can be expressed. Further, the stress Z is a value obtained by dividing the pressing force P [N] for urging the charging roller 2 against the photosensitive drum 1 by the sum of the areas dS occupied by the minute protrusions α on the surface of the surface layer 2c.
Z = P / ΣdS (4)
It can be expressed as By using the above equations (1) to (4), the value of the air gap G is
G = L (1-P / ES) (5)
Can be shown.

  When the respective parameters of the charging roller 2 of the present embodiment are inputted and calculated, the following is obtained.

L = 20 [μm], P = 9.8 [N], E = 64 [MPa], S = 1 [μm2]
G1 = 20 (1- (9.8 / (64 × 1)) = 18 [μm]
Met. On the other hand, in section 1, which is a non-image area,
G2 = 2.8 ((1- (9.8 / (64 × 0.6)) = 2.1 [μm]
Met.

FIG. 8 is a table showing the measurement result of the air gap G and the result of Expression (5) for each of the longitudinal position sections shown in FIG. As shown in the figure, the air gap G and the equation (5) are generally correlated, and in the image forming area of the charging roller 2,
L (1-P / ES)> 7.7 × 10 ⁻⁶ m
I have seen.

  As described above, the charging roller 2 is roughened only in the first surface area corresponding to the image forming area, and the composite Young's modulus of the charging roller 2 is adjusted. For this reason, even if a predetermined pressure is applied at the contact portion with the photosensitive drum 1, a gap can be maintained between the photosensitive drum 1 and the shape of the surface being maintained.

(Verification 1: Photosensitive drum scratch suppression effect verification)
The effect of suppressing scratches on the photosensitive drum 1 in the charging roller 2 of this embodiment was confirmed.

  For verification, a charging roller having a uniform roughness up to the non-image area was prepared and examined.

  As a verification method, a sheet-passing test was performed in the image forming apparatus according to the present embodiment using the charging roller 2 according to the present embodiment and a straight-shaped charging roller for comparison. The evaluation environment was a 35 ° C./90% RH environment, and the endurance test of 15000 sheets was performed under the condition of two full-color LETTER paper test images. The durability printing rate was 1%.

  The results will be described for each of the image area and the non-image area.

(Result in image area)
The scraping amount of the photosensitive drum 1 per 1000 pages was 0.8 μm in the present embodiment and the comparative example in the image area.

(Results in non-image area)
The scraping amount of the photosensitive drum 1 per 1000 pages was 0.9 μm for the charging roller 2 of the present embodiment and 1.4 μm for the charging roller of the comparative example.

In the comparative example, an image defect (a severe vertical streak image) caused by a drum scratch occurred at 13000 time point.
Further, when the photosensitive drum 1 was charged by the charging roller in the present embodiment, no moiré was confirmed in the image formed on the photosensitive drum 1 throughout the life of the process cartridge.

Thus, in the charging roller 2 of this embodiment, since the surface roughness of the non-image area is set low, the discharge area can be reduced and the discharge amount can be suppressed. As a result, while suppressing the occurrence of moire, the photoconductor scraping, especially the photoconductor end scraping that increases the scraping amount of the paper end, is reduced,
Image defects due to scratches can be suppressed.

Second Embodiment
Next, another embodiment of the present invention will be described. In the present embodiment, many parts are common to the first embodiment, and only the parts different from the first embodiment will be described below, and redundant explanations will be omitted.

  In the first embodiment, the surface roughness of the charging roller 2 is changed between the image area and the non-image area. In the present embodiment, charging is performed between the outside of the image area of the image forming apparatus and the sheet passing edge. It is characterized by changing the surface roughness of the roller.

  Generally, the amount of photoconductor drum 1 that can be scraped increases in a non-image forming portion, particularly in a paper passing end portion. This is because, in the non-image forming area described in the first embodiment, in addition to the factor that the friction coefficient between the photosensitive drum 1 and the cleaning blade 12 becomes high, the amount of paper dust generated by paper rubbing is large. Due to

That is, when the amount of paper dust present at the contact portion between the photosensitive drum 1 and the cleaning blade 12 is larger than that in other regions, these paper dusts act as an abrasive for the photosensitive drum 1 and the photosensitive drum 1 This is because the effect of shaving is promoted. For this reason, if a transition point of roughness is provided at the end of the maximum sheet passing width, 1) an increase in frictional force due to the absence of toner,
The three factors of 2) polishing with paper dust and 3) increase in the amount of scraping due to an increase in the amount of discharge accompanying an increase in the discharge area are duplicated. For this reason, the amount of increase in the shaving amount becomes significant as compared with other regions.

  In view of the above-described concerns, the present embodiment is provided on the image area side from the sheet passing end so that the sheet passing end and the roughness transition point do not overlap outside the image area. That is, the position in the longitudinal direction of the boundary between the first surface area and the second surface area is on the inner side of the position where the end in the longitudinal direction of the recording medium K passes. As a result, the effects of the factors 1) and 3) that can be removed can be limited to those described above, so that the removal is suppressed.

  FIG. 9 is a graph showing the roughness between the lengths of the charging roller 2 divided into 10 parts. FIG. 10 is a schematic diagram showing 10 divisions in the longitudinal direction of the charging roller 2 shown in FIG.

  As shown in FIGS. 9 and 10, for the sections 2 to 8 as the paper passing area, the surface ten-point average roughness Rzjis (μm) satisfies 15 ≦ Rzjis ≦ 50. The ten-point average roughness Rzjis (μm) of the surface was 21 μm.

  Further, in section 1 and section 10 which are non-sheet passing area areas, the ten-point average roughness Rzjis (μm) of the surface satisfies 15> Rzjis.

  In the charging roller 2 in the present embodiment, generation of moiré throughout the life of the process cartridge was not confirmed as in the first embodiment. Further, it was possible to reduce the abrasion of the photosensitive member, particularly the edge of the photosensitive member where the amount of abrasion at the edge of the paper increases, and to suppress image defects due to scratches.

  Further, in the first and second embodiments described above, a sine wave is applied as the waveform of the AC (alternating voltage) component of the oscillating voltage. However, the present invention is not limited to this. For example, a rectangular wave, a sawtooth wave, a triangular wave, a pulse wave, or a rectangular wave voltage formed by periodically turning on and off a DC voltage may be used. In the first embodiment and the second embodiment, the magnetic toner is used. However, the present invention is not limited to this. For example, the same effect can be obtained by using a non-magnetic toner.

  In the first embodiment and the second embodiment, the jumping development method is adopted. However, the invention is not limited to this. For example, the same effect can be obtained even if the contact development method is adopted.

  In the first embodiment and the second embodiment, the charging roller 2 is provided with a surface layer, but the present invention is not limited to this. For example, if the charging roller 2 can maintain the surface shape described in the first embodiment by curing the conductive elastic layer even if the surface layer is removed, the same effect can be obtained by applying the present invention. .

  Further, the charging roller 2 of the present invention is not limited to the first embodiment and the second embodiment. The surface shape of the charging roller 2 shown in the figure is merely an example, and other embodiments, application examples, modifications, and combinations thereof are possible as long as they do not depart from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 2 ... Charging roller 50 ... High voltage power supply 100 ... Image forming device G ... Air gap K ... Recording medium L ... Height P ... Pressing force S ... Area α protrusion

Claims (13)

A charging member that is disposed along the longitudinal direction of the image carrier of the image forming apparatus and charges the image carrier,
The charging member has a first surface region and two second surface regions, and the first surface region is disposed between the two second surface regions with respect to the longitudinal direction,
The surface of the first surface region enables discharge between the image carrier and the charging member at a contact surface with the image carrier when the charging member contacts the image carrier. It is the roughness that forms the gap,
The surface of the second surface region enables discharge between the image carrier and the charging member at a contact surface with the image carrier when the charging member contacts the image carrier. Forming a gap, the roughness being lower than the roughness of the first surface region,
The image carrier has an image forming region on the surface and a non-image forming region outside the longitudinal direction of the image forming region,
With respect to the longitudinal direction, the position of the boundary between the first surface region and the second surface region is in the vicinity of the position of the boundary between the image forming region and the non-image forming region,
The charging member according to claim 2, wherein the second surface region has a smaller amount of discharge with the image carrier than the first surface region. A charging member that is disposed along the longitudinal direction of the image carrier of the image forming apparatus and charges the image carrier,
The charging member has a first surface region and two second surface regions, and the first surface region is disposed between the two second surface regions with respect to the longitudinal direction,
The surface of the first surface region enables discharge between the image carrier and the charging member at a contact surface with the image carrier when the charging member contacts the image carrier. It is the roughness that forms the gap,
The surface of the second surface region enables discharge between the image carrier and the charging member at a contact surface with the image carrier when the charging member contacts the image carrier. Forming a gap, the roughness being lower than the roughness of the first surface region,
The second surface region has a smaller discharge amount with the image carrier than the first surface region,
The image forming apparatus is configured such that a sheet-like recording medium is conveyed to the surface of the image carrier and a developer image is transferred to the recording medium.
The charging member characterized in that the position in the longitudinal direction of the boundary between the first surface area and the second surface area is inside the position through which the end in the longitudinal direction of the recording medium passes. . A charging member that is disposed along the longitudinal direction of the image carrier of the image forming apparatus and charges the image carrier,
The charging member has a first surface region and two second surface regions, and the first surface region is disposed between the two second surface regions with respect to the longitudinal direction,
The surface of the first surface region enables discharge between the image carrier and the charging member at a contact surface with the image carrier when the charging member contacts the image carrier. It is the roughness that forms the gap,
The surface of the second surface region enables discharge between the image carrier and the charging member at a contact surface with the image carrier when the charging member contacts the image carrier. Forming a gap, the roughness being lower than the roughness of the first surface region,
The second surface region has a smaller discharge amount with the image carrier than the first surface region,
The longitudinal position of the boundary between the first surface area and the second surface area is the longitudinal position of the boundary between the image forming area and the non-image forming area and the longitudinal direction of the recording medium. A charging member characterized by being between the position of the end portion in the direction. 4. The charging member according to claim 2, wherein an end portion in the longitudinal direction of the recording medium is an end portion of the recording medium having a maximum sheet passing width. The charging member has a surface hardness of 50 ° to 85 ° as Asker C hardness,
The ten-point average roughness Rzjis of the first surface region is 15 (μm) ≦ Rzjis ≦ 50 (μm), and the ten-point average roughness Rzjis of the second surface region is 15 (μm)> Rzjis ( the charging member according to any one of claims 1 to 3, characterized in that it is [mu] m). The charging member according to any one of claims 1 to 3 , wherein the non-image forming area is more rapidly scraped than the image forming area. A charging member that is disposed along the longitudinal direction of the image carrier of the image forming apparatus and charges the image carrier,
The charging member has a first surface region and two second surface regions, and the first surface region is disposed between the two second surface regions with respect to the longitudinal direction,
The surface of the first surface region enables discharge between the image carrier and the charging member at a contact surface with the image carrier when the charging member contacts the image carrier. It is the roughness that forms the gap,
The surface of the second surface region enables discharge between the image carrier and the charging member at a contact surface with the image carrier when the charging member contacts the image carrier. Forming a gap, the roughness being lower than the roughness of the first surface region,
The second surface region has a smaller discharge amount with the image carrier than the first surface region,
The charging member is
A conductive support;
An elastic layer provided around the conductive support;
A plurality of microprojections formed on the surface of the elastic layer in contact with the image carrier;
Have
P (N) is a pressing force for pressing the charging member against the image carrier, L (m) is a height before the minute protrusion is elastically deformed, and the surface of the charging member is occupied by the minute protrusion. When the area to be S is (m2) and the Young's modulus when the elastic layer is deformed is E (MPa),
In the first surface region,
L (1-P / ES)> 7.7 × 10 ⁻⁶ (m)
The filling,
In the second surface region,
L (1-P / ES) <7.7 × 10 ⁻⁶ (m)
A charging member characterized by satisfying   The charging member according to claim 7, wherein the fine protrusion is formed by containing fine particles as a surface roughening agent.   The charging member according to claim 7, wherein the minute protrusion has a surface roughness formed by foaming.   The charging member according to any one of claims 1 to 9, wherein the charging member has a roller shape that can be rotatably held. A process cartridge that can be attached to and detached from an image forming apparatus,
The charging member according to any one of claims 1 to 10,
A process cartridge comprising the image carrier. An image forming apparatus to which the process cartridge according to claim 11 is attached,
An image forming apparatus comprising a power source for applying a voltage to the charging member. The image forming apparatus according to claim 12 , wherein the power source applies an AC voltage to the charging member.

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