JP2012123281A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of the problem of causing ITB damage due to a carrier by minimizing a downtime.SOLUTION: An image forming apparatus includes a mechanism for separating a photoreceptor and an intermediate transfer body and changes the control of the separation mechanism, according to temperature and humidity or the rotation time of a developing unit. The respective rotary axes of an upstream regulating roller 58 and primary transfer rollers 53a, 53b and 53c are fixed to a common retract frame 581. The upstream regulating roller 58 is connected to a grounding potential. The primary transfer rollers are insulated from the retract frame 581 and configured so that an independent primary transfer bias voltage can be applied to each of the primary transfer rollers. The retract frame 581 is vertically moved while keeping parallel relation by rotating a cam 582 rotated around a rotary axis 584 and a cam 583 rotated around a rotary axis 585 in parallel. The sagging of an intermediate transfer belt 51 due to the moving up and down of the retract frame 581 is absorbed by the movement of a tension roller 55.

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, or a fax machine.

  2. Description of the Related Art An image forming apparatus that forms a full-color image by transferring a toner image for each separated color formed on a photosensitive drum in an overlapping manner on an intermediate transfer belt has been put into practical use. An image forming apparatus that forms a full-color image by superimposing and transferring toner images of different separation colors on a recording material sucked and conveyed by a recording material conveyance belt has also been put into practical use. A full-color image forming apparatus using only a photosensitive drum for forming a black toner image has been put to practical use when a black and white image is formed by disposing a photosensitive drum for forming a black toner image on the most downstream side.

  Patent Documents 1 to 3 show an image forming apparatus in which a belt member is separated from an image carrier that forms a separated color toner image other than black, and a black and white image is formed by the most downstream photosensitive drum. Unnecessary mechanical wear and power consumption are saved by separating the belt member and stopping unrelated photosensitive drums and charging devices.

  Patent Document 1 discloses a contact / separation mechanism for a belt member that integrally moves three transfer rollers that support the inner surface of the belt member using an eccentric cam. Patent Document 3 discloses a contact / separation mechanism for a belt member in which a transfer roller of a plurality of photosensitive drums is pivotally supported on a plate member rotated around a rotation axis of a support roller.

JP 2001-249519 A JP 2004-117426 A JP 2005-62642 A JP 2000-298408 A JP 2006-119508 A JP 2004-317915 A

  Conventionally, an image forming apparatus that includes a plurality of image forming units, forms toner images of different colors in each image forming unit, and sequentially superimposes and transfers the toner images on the same recording material to form a color image Various proposals have been made.

  FIG. 1 is an overall schematic diagram of an image forming apparatus. A description will be given using an image forming apparatus of a tandem type and an intermediate transfer type. This image forming apparatus has a configuration in which image forming units corresponding to different colors are continuously arranged along a flat surface portion of an intermediate transfer belt as an intermediate transfer member as an image receiving member. In this embodiment, the image forming units UY, UM, UC, and UBk for yellow, magenta, cyan, and black toner are arranged and basically have the same configuration. Therefore, the following description of the image forming unit will be made only for the yellow image forming unit UY.

  In the yellow image forming unit UY in FIG. 1, the photosensitive drum 1y is a cylindrical photosensitive drum, and is driven to rotate in the direction of arrow a. The charging means 2y is pressed against the surface of the photosensitive drum 1y. The charging unit 2y rotates with the rotation of the photosensitive drum 1y, and a voltage is applied to charge the surface of the photosensitive drum 1y to a desired potential.

  Next, the photosensitive drum 1y is exposed by the latent image means 3y according to the recorded image information. The exposure is performed by a laser beam scanner / LED or the like.

  The developing unit 4y includes a developing roller 4y1 that conveys toner as a developer to the surface of the photosensitive drum 1y, a developer supply roller 4y2 for re-applying toner to the surface of the developing roller 4y1, and the toner on the developing roller 4y1. It is composed of a developer regulating blade 4y3 for regulating the coating amount.

  The developing roller 4y1 whose surface is uniformly coated with the toner by the developer regulating blade 4y3 is lightly pressed against the photosensitive drum 1y, rotated in the forward direction, and further applied with a voltage, thereby forming a latent image on the photosensitive drum 1y. It is visualized as a toner image.

  The toner image formed on the photosensitive drum 1y is conveyed to a primary transfer portion formed between the intermediate transfer belt 5 and the photosensitive drum 1y as the photosensitive drum 1y rotates.

  The intermediate transfer belt 5 has an endless sheet belt shape. In this embodiment, the intermediate transfer belt 5 is stretched by the driving roller 6 and the stretching rollers 7 a and 7 b, and is driven in the direction of the arrow c by the drive given from the driving roller 6.

  The photosensitive drum 1y is pressed against a primary transfer roller 8y as a primary transfer unit via the intermediate transfer belt 5 to form a primary transfer portion. In this embodiment, as the primary transfer roller 8y, a roller shape having an elastic rubber layer on a metal core is used. However, a sheet, blade, or brush shape can also be used.

  The toner image formed on the photosensitive drum 1y is conveyed to a primary transfer portion formed between the intermediate transfer belt 5 and the photosensitive drum 1y as the photosensitive drum 1y rotates. Therefore, the image is transferred to the surface of the intermediate transfer belt 5 by the primary transfer voltage applied to the primary transfer roller 8y.

  The full-color toner image formed on the intermediate transfer belt 5 is conveyed to a secondary transfer portion formed by a secondary transfer roller 9 serving as a secondary transfer unit and the intermediate transfer belt 5. In synchronization with this, the transfer material P is fed from the paper feeding unit 10, and at the same time, a predetermined voltage is applied to the secondary transfer roller 9 to transfer the toner image to the transfer material P.

  The transfer material P onto which the full-color toner image has been transferred is conveyed to the fixing unit 11, where the toner image is fixed on the transfer paper P by the action of heat and pressure, and is discharged out of the apparatus.

  Note that the image forming apparatus according to the present exemplary embodiment includes an exposure unit for static elimination for eliminating the residual potential of the photosensitive drum after the primary transfer. The neutralizing LEDs 16y as the neutralizing exposure means are respectively arranged at positions where the surface of the photosensitive drum 1y after the primary transfer is irradiated. In this embodiment, an LED is used as the exposure means for static elimination. However, it is possible to irradiate laser light, analog light such as a halogen lamp, or light that has been converted to monochromatic light using a filter or a diffraction grating. Good.

  Further, the transfer residual toner after the completion of the primary transfer is cleaned by the photosensitive drum cleaner 13y, and the residual toner on the intermediate transfer body after the secondary transfer is removed by the intermediate transfer belt cleaner 12.

  The developer used in the developing devices 1a to 1d will be described.

  The developing device carries a dry developer on a developing sleeve which is a developer carrying member, conveys the developer to the surface of the photosensitive drum by rotation of the developing sleeve, and an alternating electric field between the developing sleeve and the photosensitive drum. A method for visualizing an electrostatic latent image on a photosensitive drum with a conveyed developer while applying a voltage is well known.

  As a developing method, for example, a magnetic brush of a two-component developer composed of carrier particles and toner particles is formed by a magnetic force on the surface of a developing sleeve having a magnet disposed inside, and this magnetic brush is spaced from the developing sleeve at a slight interval. By transferring or reversing the toner from the magnetic brush on the developing sleeve to the photosensitive drum by applying an alternating electric field between the developing sleeve and the photosensitive drum (SD gap) by rubbing or approaching the photosensitive drum held and opposed. A so-called magnetic brush development method in which development is performed repeatedly is known (see, for example, Japanese Patent Laid-Open Nos. 55-3202082 and 59-165082).

  Also known are non-contact type alternating electric field development methods using a two-component developer for the purpose of simple color development and multiple development (for example, Japanese Patent Laid-Open Nos. 56-14268 and 58-68051). JP-A 56-144442, JP-A 59-181362, JP-A 60-176069).

  By the way, magnetic metal oxides have been conventionally used for magnetic carrier particles used in the two-component developer. Ideally, these carrier particles should be mixed with toner particles to form a magnetic brush on the developing sleeve, and only the toner particles should be transferred onto the photosensitive drum by the action of the developing electric field. However, the carrier particles are also transferred onto the photosensitive drum.

  By the way, in the carrier adhesion, the electrostatic force due to the fog removal potential (the potential difference between the DC bias applied to the developing sleeve 21 and the surface potential of the photosensitive drum 1 (non-image portion potential)) is magnetized in the non-image portion on the photosensitive drum 1. Occurs to overcome power. The fog removal potential is an electric field in a direction in which the fog toner is pulled back from the photosensitive drum 1 to the developing sleeve 21, and a carrier having a polarity opposite to that of the toner is an electric field in a direction in which the carrier is attracted in the direction of the photosensitive drum 1. Figure 2 shows the relationship. Usually, the fog removal potential is set to a value at which both become optimum values, such as the range of the fog removal potential setting region. That is, even with a normal fog removal potential, a small amount of fog toner and carrier adhesion actually occur.

  Incidentally, a rubber blade is generally used for the cleaning blade on the photosensitive drum. However, in a cleaning device having such a cleaning blade, a transfer residue that is scraped off by the cleaning blade and stays in the vicinity of the edge portion. By interposing the toner, the frictional force is reduced, thereby obtaining a stable and good cleaning performance without the cleaning blade being bent.

  That is, a small amount of fog toner exists also in the non-image region, and thus plays a role as the above-described lubricant.

  In order to reduce the amount of carrier adhesion at the time of stopping or starting, Japanese Patent Laid-Open No. 2001-092197 discloses a method for cutting the charging bias and the developing bias for the purpose of suppressing the amount of carrier adhesion at the time of stopping the apparatus. Although a configuration in which the charging bias and the developing bias are reduced on the slope while keeping the fog removal potential constant is disclosed, a small amount of carrier adhesion occurs as described above.

  This phenomenon may occur in the entire width in which the developer (magnetic carrier) exists, that is, the normal development effective width is designed to be sufficiently larger than the image width, so that the width of the intermediate transfer belt 130 is almost the same. Occurs throughout.

  By the way, the magnetic carrier transferred to the photosensitive drum may cause a rubbing scratch on the transport belt 130 made of a resin sheet by rubbing against the transfer belt at the transfer portion.

  This phenomenon occurs more noticeably at the time of starting and stopping the rotation.

  Normally, the photosensitive drum and the conveyor belt are rotated without a difference in peripheral speed, but at the time of starting and stopping, a difference in peripheral speed is larger than usual due to the difference between the rising speed and the falling speed.

  As described above, even when the operation is stopped normally, a small amount of carrier adhering to the photosensitive drum when the apparatus is stopped is sandwiched in the transfer nip by the fog removal potential. Therefore, the carrier and the drum are rubbed at the transfer nip portion at the time of activation, and scratches are generated.

  Depending on the size and depth of the intermediate transfer belt, the rubbing scratches on the intermediate transfer belt may cause backside staining of the image or transfer failure due to poor cleaning of the intermediate transfer belt.

  The object of the present invention is to suppress sliding scratches on the intermediate transfer belt at the time of start / stop by the magnetic carrier in the two-component developer, and prevent image back-dirt and transfer failure due to poor cleaning of these belts, An object of the present invention is to provide an image forming apparatus capable of obtaining an image of good quality.

A plurality of first image carriers on which electrostatic latent images are formed;
A plurality of developing means for developing the electrostatic latent image as developer images of different colors;
A second image carrier to which developer images of different colors formed on the plurality of first image carriers are transferred;
Primary transfer means for charging the second image carrier;
Secondary transfer means for collectively transferring the developer images transferred onto the second image carrier onto the recording medium;
A recording unit that includes a separating unit that separates the second image carrier and the first image carrier, and that detects and records the rotation time of the developing unit;
In an image forming apparatus having a temperature / humidity detecting means for detecting the temperature / humidity of outside air,
The operation timing of the separation means at the start of the job is changed according to the rotation time of the temperature / humidity detection means or the development means.

  When the separation means is changed, the separation operation at the end of the job is also changed.

  With the configuration described above, it is possible to minimize downtime and prevent problems caused by ITB scratches caused by carriers.

Overall schematic diagram of image forming apparatus Diagram showing the relationship between fog toner amount / carrier adhesion amount and fog removal potential Explanatory drawing which shows the structure of the tandem type full-color image forming apparatus used in the implementation system FIG. 3 is an explanatory diagram showing a configuration of an image forming unit for each separation color of the tandem type full color image forming apparatus of FIG. Explanatory drawing of attachment / detachment mechanism of intermediate transfer belt and support roller Control flowchart

  Hereinafter, a full-color image forming apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. The image forming apparatus of the present invention is not limited to the limited configuration of the embodiments described below. As long as the support roller is separated on the downstream side of the photosensitive drum to avoid an electrical influence on the intermediate transfer belt or the like, a part or all of the configuration of each embodiment is replaced with another alternative configuration. It can also be realized in the embodiment.

  In the present embodiment, a tandem image forming apparatus in which four photosensitive drums 1a, 1b, 1c, and 1d are arranged along the intermediate transfer belt 51 will be described. However, the image forming apparatus of the present invention may be an image forming apparatus in which four or more photosensitive drums including intermediate colors are arranged along the recording material conveyance belt, or may be a monochrome specification with one photosensitive drum. That is, in the present embodiment, details of the operation in the black single color mode in the apparatus for forming four color images of yellow, magenta, cyan, and black will be described. However, this configuration can also be applied to an image forming apparatus using colors other than the four colors or an image forming apparatus using light color toner.

  The image forming apparatus of the present invention can be implemented in accordance with various uses such as a printer, various printing machines, a copying machine, a FAX, and a multifunction machine.

  It should be noted that the configuration of the image forming apparatus, the mounted power supplies, the detailed structure of the apparatus, the control, and the like disclosed in Patent Documents 1 to 6 are not illustrated and detailed description is omitted in order to avoid repeated complications. Omitted.

<Image forming apparatus>
FIG. 3 is an explanatory diagram showing the configuration of the tandem type full-color image forming apparatus used in this embodiment, and FIG. 4 is an explanatory diagram showing the configuration of the image forming unit for each separation color. As shown in FIG. 4, the image forming apparatus 100 is an intermediate transfer type tandem full color image forming apparatus in which unitized image forming portions Sa, Sb, Sc, and Sd are arranged along an intermediate transfer belt 51. The image forming units Sa, Sb, Sc, and Sd have photosensitive drums 1a, 1b, 1c, and 1d, respectively, and form yellow, magenta, cyan, and black separated color toner images by an electrophotographic process.

  The image forming portions Sa, Sb, Sc, and Sd are configured in common except that the color of the developer (toner) filled in the developing devices 4a, 4b, 4c, and 4d is different. Therefore, the detailed structure of the image forming portions Sa, Sb, Sc, and Sd will be described in common with reference to FIG. 3 that is generally illustrated except for the subscripts a, b, c, and d.

  As shown in FIG. 3, each of the image forming sections S (Sa, Sb, Sc, Sd) has a photosensitive drum 1 (1a, 1b, 1c, 1d) as an image carrier. Surrounding the photosensitive drum 1 rotating in the arrow R1 direction, a primary charging roller 2, an exposure device 3, a developing device 4, a primary transfer roller 53, and a cleaning device 6 are sequentially arranged in the arrow R1 direction.

  The photosensitive drum 1 is a cylindrical electrophotographic photosensitive member in which a photoconductive layer 12 is formed on the outer periphery of a conductive substrate 11 such as aluminum, and the charging polarity of the surface is negative. The photosensitive drum 1 is rotatably supported by a central support shaft 13 and is rotationally driven by a driving source (not shown).

  The primary charging roller 2 is pressed against the photosensitive drum 1 while being charged with a charging bias voltage by a charging bias power source 24 and is driven to rotate in the direction of the arrow R2, thereby charging the surface of the photosensitive drum 1 to a predetermined negative potential. Let The primary charging roller 2 is configured in a roller shape as a whole by placing a conductive metal core 21 at the center of a low resistance conductive layer 22 made of a conductive foam material as a rotating shaft and covering an outer periphery with a medium resistance conductive layer 23. ing. Both ends of the cored bar 21 are rotatably supported by a bearing member (not shown) and are urged toward the photosensitive drum 1 by a pressing spring (not shown), so that the primary charging roller 2 is a surface of the photosensitive drum 1. Are pressed against each other with a predetermined pressing force.

  The exposure device 3 scans and exposes the surface of the photosensitive drum 1 by scanning a laser beam pulse-modulated with an image signal obtained by developing image data along a scanning line by a polygon mirror (not shown). A potential corresponding to the pixel density is written along the exposure scanning line on the uniformly charged surface of the photosensitive drum 1, and an electrostatic latent image is formed on the surface of the photosensitive drum 1.

  The developing device 4 develops a toner image by attaching a developer to the electrostatic latent image on the surface of the photosensitive drum 1. The developing container 41 contains a two-component developer in which non-magnetic toner particles (toner) and magnetic carrier particles (carrier) are mixed. The developing container 41 is divided into a developing chamber 45 and a stirring chamber 46, and a replenishing chamber 47 containing replenishing toner is connected above the stirring chamber 46.

  A developing sleeve 42 is rotatably installed in an opening portion of the developing container 41 facing the photosensitive drum 1, and a magnet roller 43 is fixedly disposed inside the developing sleeve 42 so as not to rotate. The two-component developer carried on the developing sleeve 42 by the magnetic field of the magnet roller 43 is regulated to a thin layer by the regulating blade 44 as the developing sleeve 42 rotates, and is supplied to the developing region facing the surface of the photosensitive drum 1. Is done. In the developing region, the two-component developer is raised by the magnetic field of the magnet roller 43 to form a magnetic brush, and the surface of the photosensitive drum 1 is rubbed by the magnetic brush. Since the developing bias voltage is applied to the developing sleeve 42 by the developing bias power source 48, the toner adhering to the carrier constituting the ears of the magnetic brush electrostatically moves to the electrostatic latent image on the photosensitive drum 1. Adhere. Here, a toner image is formed by reversal development in which toner charged to the same polarity (negative polarity) as the charging polarity of the photosensitive drum 1 is attached to a portion where the negative potential is attenuated by exposure of the surface of the photosensitive drum 1. .

  The toner image formed on the surface of the photosensitive drum 1 is primarily transferred to the intermediate transfer belt 51 charged using the primary transfer roller 53. In the primary transfer roller 53, a cylindrical conductive layer 532 is covered on the outer peripheral surface of a core metal 531 that also serves as a rotation shaft. The conductive layer 532 is pressed against the photosensitive drum 1 with a predetermined pressing force via the intermediate transfer belt 51 by urging both end portions of the core metal 531 that is rotatably supported by a spring member (not shown). The primary transfer roller 53 is in pressure contact with the inner surface of the intermediate transfer belt 51, and is driven to rotate as the intermediate transfer belt 51 moves.

  The primary transfer roller 53 forms a primary transfer portion N <b> 1 between the intermediate transfer belt 51 and the photosensitive drum 1 by connecting a primary transfer bias power source 54 to the metal core 531 and applying a primary transfer bias voltage. A primary transfer bias voltage having a polarity (positive polarity) opposite to the normal charging polarity (negative polarity) of the toner is applied to the primary transfer roller 53 during primary transfer of the toner image. An electric field is formed between the primary transfer roller 53 and the photosensitive drum 1 to urge negatively charged toner particles on the surface of the photosensitive drum 1 toward the intermediate transfer belt 51. The photosensitive drum 1 moves to the intermediate transfer belt 51.

  Transfer residual toner or the like that has not been primarily transferred by the primary transfer portion N1 is removed by the cleaning device 6 so that the surface of the photosensitive drum 1 is prepared for the next primary charging to primary transfer process. The cleaning device 6 causes a cleaning blade 61 made of a flexible elastic material to slide on the surface of the photosensitive drum 1 and scrapes off deposits on the surface of the photosensitive drum 1 to the drum cleaner housing 63. The waste toner accumulated in the drum cleaner housing 63 is transported in the axial direction by the transport screw 62 and stored in a waste toner storage unit (not shown).

  As shown in FIG. 3, the intermediate transfer belt 51 is disposed in pressure contact with the image forming portions Sa, Sb, Sc, and Sd in common. The four separated color toner images formed by the photosensitive drums 1a, 1b, 1c, and 1d are primarily transferred onto the intermediate transfer belt 51 and transferred to the secondary transfer unit N2, and the secondary transfer unit N2 records the recording material. Secondary transfer is performed collectively on P.

  The intermediate transfer belt 51 is gathered together in the intermediate transfer unit 5 in a state where it is supported by being driven by a driving roller 52, a driven roller 55, a secondary transfer inner roller 56, and an upstream regulating roller 58. The intermediate transfer belt 51 is driven by a driving roller 52 connected to a driving source (not shown) and circulates in the direction of the arrow R3 to rotate the pressure-sensitive photosensitive drums 1a, 1b, 1c, and 1d. The intermediate transfer belt 51 is pressed on the inner surface by the primary transfer rollers 53a, 53b, 53c, and 53d, so that the outer surface is pressed against the photosensitive drums 1a, 1b, 1c, and 1d and the primary transfer portions N1a, N1b, and N1c. , N1d.

  A secondary transfer outer roller 57 facing the secondary transfer inner roller 56 with the intermediate transfer belt 51 interposed therebetween is pressed against the intermediate transfer belt 51 to form a secondary transfer portion N2. The recording material supply unit 8 supplies the recording material P to the secondary transfer unit N2 at a timing synchronized with the toner image on the intermediate transfer belt 51. That is, the recording material P is taken out one by one from the cassette 81 storing the recording material P by the pickup roller 82 and is put on standby by the registration roller 83. Then, the registration roller 83 is operated in synchronization with the head of the toner image on the intermediate transfer belt 51 to deliver the recording material P to the secondary transfer portion N2. The recording material P passes through the secondary transfer portion N2 at a speed equal to the circulation speed of the intermediate transfer belt 51, and the toner image on the intermediate transfer belt 51 is secondarily transferred.

  A secondary transfer bias power source 60 is connected to the secondary transfer outer roller 57, and in the secondary transfer of the toner image, the secondary transfer having a polarity (positive polarity) opposite to the normal charging polarity (negative polarity) of the toner is performed. A bias voltage is applied. As a result, negative toner particles on the intermediate transfer belt 51 are placed between the secondary transfer inner roller 56 connected to the ground potential and the secondary transfer outer roller 57 to which the secondary transfer bias voltage is applied. An electric field that urges toward the recording material P is formed. As the toner particles in response to the electric field move from the intermediate transfer belt 51 to the recording material P, yellow, magenta, cyan, and black separated toner images are collectively transferred to the recording material P.

  The recording material P on which the full-color toner image has been secondarily transferred through the secondary transfer portion N2 is conveyed to the fixing device 7. The fixing device 7 includes a fixing roller 71 that is rotatably arranged, and a pressure roller 72 that rotates while being in pressure contact with the fixing roller 71. A halogen lamp heater 73 is disposed inside the fixing roller 71, and the temperature of the surface of the fixing roller 71 is adjusted by controlling the power supplied to the heater 73. The recording material P transported to the fixing device 7 is pressurized and heated at a substantially constant pressure and temperature from the front and back surfaces in the process of passing through the pressure nip between the fixing roller 71 and the pressure roller 72 rotating at a constant speed. The As a result, the unfixed toner image on the surface of the recording material P is melted and fixed on the recording material P to form a full-color image.

  The residual transfer toner remaining on the intermediate transfer belt 51 without being secondarily transferred to the recording material P in the secondary transfer portion N2 is transported to the belt cleaning device 59 as the intermediate transfer belt 51 circulates, and is removed and collected. . Similar to the cleaning device 6, the belt cleaning device 59 scrapes off the transfer residual toner to the drum cleaner housing by using the cleaning blade, conveys it by the conveying screw, and stores it in the waste toner accommodating portion.

  In this embodiment, the process speed, that is, the peripheral speed of the photosensitive drum 1 and the intermediate transfer belt 51 is 100 mm / sec. The intermediate transfer belt 51 can be made of a dielectric resin such as PC (polycarbonate), PET (polyethylene terephthalate), PVDF (polyvinylidene fluoride). In this embodiment, a surface resistivity of 1012 Ω / □ (using a probe conforming to JIS-K6911 method, applied voltage of 100 V, applied time of 60 sec, 23 ° C./50% RH), formed of PI (polyimide) resin having a thickness of 100 μm Was used. However, the present invention is not limited to this, and other materials, volume resistivity, and thickness may be used.

  The primary transfer roller 53 is constituted by a core metal 531 having an outer diameter of 8 mm and a conductive urethane sponge layer 532 having a thickness of 4 mm. The electrical resistance value of the primary transfer roller 53 is about 105Ω (23 ° C./50% RH). It is. The electrical resistance value of the primary transfer roller 53 is such that the primary transfer roller 53 brought into contact with a metal roller grounded under a load of 500 g is rotated at a peripheral speed of 50 mm / sec, and a voltage of 100 V is applied to the core metal 531. It calculated | required from the electric current value measured by applying.

  The secondary transfer inner roller 56 includes a cored bar 561 having an outer diameter of 18 mm and a solid layer 562 of conductive silicon rubber having a thickness of 2 mm. The electrical resistance value of the secondary transfer inner roller 56 is determined by the primary transfer roller. It is measured to be about 104Ω in the same manner as 53.

  The secondary transfer outer roller 57 is composed of a core metal 571 having an outer diameter of 20 mm and a conductive EPDM rubber sponge layer 572 having a thickness of 4 mm. The electrical resistance value of the secondary transfer outer roller 57 is determined by the primary transfer roller. It is measured to be about 108Ω in the same manner as 53. However, the applied voltage at the time of measurement was 2000V.

<First Embodiment>
FIG. 5 is an explanatory diagram of an attaching / detaching mechanism for the intermediate transfer belt and the support roller.

  As shown in FIG. 5, the upstream regulating roller 58 moves between the raised position 58a and the lowered position 58b to raise and lower the intermediate transfer belt 51, whereby the photosensitive drums 1a, 1b, 1c, the intermediate transfer belt 51, and the like. To control the pressure contact / separation. The upstream regulating roller 58 supports the inner surface of the intermediate transfer belt 51 at the ascending position 58 a and forms a linear portion of the intermediate transfer belt 51 with the driving roller 52, so that the photosensitive drum 1 a and the intermediate transfer belt 51 The contact state and the contact position are ensured to be constant.

  When the intermediate transfer belt 51 is lowered and separated from the photosensitive drums 1 a, 1 b, and 1 c, the regulating roller 90 supports the inner surface of the intermediate transfer belt 51 at the raised position 90 b, and between the photosensitive drum 1 d and the intermediate transfer belt 51. Ensure a constant contact state and position. However, when the intermediate transfer belt 51 is pressed against the photosensitive drums 1a, 1b, and 1c, the intermediate transfer belt 51 moves to the lowered position 90a and is separated from the intermediate transfer belt 51.

  As shown in FIG. 4, the upstream regulating roller 58 and the primary transfer rollers 53 a, 53 b, and 53 c are fixed to a common retract frame 581 with their respective rotation axes. The upstream regulating roller 58 is connected to the ground potential. However, the primary transfer rollers 53a, 53b, and 53c are insulated from the retract frame 581 so that independent primary transfer bias voltages can be applied thereto.

  The retract frame 581 moves up and down while maintaining parallelism by rotating in parallel a cam 582 that rotates about the rotation shaft 584 and a cam 583 that rotates about the rotation shaft 585. The slack of the intermediate transfer belt 51 accompanying the raising and lowering of the retract frame 581 is absorbed by the movement of the tension roller 55. Since the positional relationship of the belt cleaning device 59 is fixed to the tension roller 55, the relationship between the belt cleaning device 59 and the intermediate transfer belt 51 is kept constant even when the tension roller 55 moves.

  The rotary shafts 584, 585, and 904 are rotationally driven in parallel by an unillustrated interlocking mechanism that is driven by a motor 905. In the process of rotating the rotating shafts 584 and 585 clockwise in the drawing to stop the upstream restricting roller 58 at the raised position 58a, the interlocking mechanism rotates the rotating shaft 904 in the opposite direction to move the restricting roller 90 to the lowered position 90a. To stop. In the process of rotating the rotating shafts 584 and 585 counterclockwise in the drawing to stop the upstream regulating roller 58 at the lowered position 58b, the interlocking mechanism rotates the rotating shaft 904 in the opposite direction to raise the regulating roller 90 to the raised position 90b. To stop.

  On the other hand, in conjunction with 53a, 53b and 53c, there is also a mechanism for separating the primary transfer roller 53d independently. (Full separation mode).

In this embodiment, the primary transfer all-separation mode operating conditions in the image forming operation have the following two configurations: (1) ITB, the primary transfer roller is attached before the drum drive starts, and at that time, the JOB ends (2) ITB, operate the primary transfer roller separation mode before starting the drum drive, and place the primary transfer roller in the attached state after the start of driving.

  In order to avoid carrier scratches at the time of start-up, the configuration (2) is operated under the following conditions in which the carrier adhesion on the drum is significantly large.

  This prevents the carrier from being damaged by the carrier sandwiched between the drum-ITB nip when stopped.

  In general, it is known that the carrier adhesion amount increases when the CRG endurance is in the initial stage and when it is in a high temperature and high humidity environment. This is because, in the initial stage of CRG, the small diameter component contained in the carrier is easily discharged, and carrier adhesion is likely to occur even at high temperature and high humidity with a small charge amount.

Therefore, in this example, switching between (1) and (2) was performed under the following conditions.
・ When the number of CRG passes is 5K or less → (2)
・ When the outside environment is high temperature and humidity → (2)
・ Other than that → (1)
The control flow is shown in FIG.

  When the job starts, the above conditions are determined, and the controls (1) and (2) are selected to start the image forming operation.

  In other words, under conditions where there is a large amount of carrier adhesion and the occurrence of rubbing scratches, the rubbing scratches can be prevented by bringing the primary transfer roller, the intermediate transfer belt and the drum into a non-contact state at the start of driving.

  By the operation procedure as described above, it is possible to prevent the carrier from being rubbed due to the difference in peripheral speed when the drum and the belt are driven under the condition where the carrier adheres frequently.

Image forming section S (Sa, Sb, Sc, Sd)
Photosensitive drum 1 (1a, 1b, 1c, 1d)

Claims (2)

A plurality of first image carriers on which electrostatic latent images are formed;
A plurality of developing means for developing the electrostatic latent image as developer images of different colors;
A second image carrier to which developer images of different colors formed on the plurality of first image carriers are transferred;
Primary transfer means for charging the second image carrier;
Secondary transfer means for collectively transferring the developer images transferred onto the second image carrier onto the recording medium;
A recording means for detecting and recording the rotation time of the developing means; and a temperature / humidity detection for detecting the temperature / humidity of the outside air; and a separation means for separating the second image carrier from the first image carrier. In an image forming apparatus having means,
An image forming apparatus characterized in that the operation timing of the separating means at the start of a job is changed according to the rotation time of the temperature / humidity detecting means or developing means. The image forming apparatus according to claim 1, wherein when the separation unit is changed, a separation operation at the end of the job is also changed.