JP2013217974A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten an intermediate transfer body and thereby, to allow designing an image forming apparatus smaller in size, in an image forming apparatus which sequentially forms toner images of a plurality of colors on a single photosensitive drum, and sequentially transfers and overlaps the images onto an intermediate transfer body by supplying a current from a secondary transfer roller.SOLUTION: The image forming apparatus having an intermediate transfer body 6 is configured to satisfy DI>M, where M represents the maximum length of a transfer material P to be output and DI represents a distance along an outer circumferential face of the intermediate transfer body from a primary transfer part T1 to a bias supply member 10 with respect to the rotation direction of the intermediate transfer body 6, to satisfy SD>M, where SD represents a distance along the outer circumferential face of the intermediate transfer body from the secondary transfer member 7 to the primary transfer part T1, and to satisfy IS>M, where IS represents a distance along the outer circumferential face of the intermediate transfer body from the bias supply member 10 to the secondary transfer member 7. The apparatus is further configured to satisfy L>3M/2, where L represents a perimeter of the intermediate transfer body 6. By applying a voltage to the secondary transfer member 7 or the bias supply member 10, a toner image on an image carrier 1 is transferred onto the intermediate transfer body 6.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that forms an image by electrophotography.

  As one of electrophotographic color image forming apparatuses, one having a configuration in which a plurality of developing devices are provided for one photosensitive drum is known in order to reduce the size and cost of the apparatus. In such an image forming apparatus, each color image is sequentially transferred to an intermediate transfer belt, and all images are transferred to an intermediate transfer member such as an intermediate transfer belt, and then a toner image is transferred to a transfer material in a lump.

  FIG. 20 is a schematic view showing a conventional color image forming apparatus 100.

  The color image forming apparatus 100 includes a photosensitive drum 1 as an image carrier, and the photosensitive drum 1 is uniformly charged by a charging member 2. Thereafter, an electrostatic latent image corresponding to the formed image is formed on the photosensitive drum 1 by the exposure device 3. The rotary 4 supporting the developing devices 4a, 4b, 4c, and 4d rotates on the electrostatic latent image, and toner is supplied by the corresponding developing devices 4a, 4b, 4c, and 4d, and the toner is transferred onto the photosensitive drum 1. Visualize as an image.

  A toner image developed on the photosensitive drum 1 for each color is subjected to a primary transfer roller 14 (primary transfer roller 14) in which a primary transfer voltage is applied from a high-voltage power supply 15 to an intermediate transfer belt 6 that is opposed to and contacted at a primary transfer portion T 1. Member). The toner image primarily transferred to the intermediate transfer belt 6 is secondarily transferred onto the transfer material P by a secondary transfer roller (secondary transfer member) 7 to which a secondary transfer voltage is applied by a high voltage power source 8.

  As described above, in the configuration of the conventional color image forming apparatus 100 shown in FIG. 20, two high-voltage power supplies are necessary to perform the primary transfer and the secondary transfer. For this reason, there are disadvantages that cost and space are required, and there are many cost and space losses.

  On the other hand, in Patent Document 1 shown in FIG. 21, in a full-color image forming apparatus having a configuration of an intermediate transfer drum 6 using one photosensitive drum 1 and an aluminum base layer, one transfer is performed for primary transfer and secondary transfer. The power supply is reduced by applying a bias from the power supply. That is, a method is described in which the power supply is reduced by switching and supplying the primary transfer bias to the aluminum base layer of the intermediate transfer drum 6 and the secondary transfer bias to the secondary transfer roller from one power supply.

  Further, in Patent Document 2 shown in FIG. 22, a full color having a configuration of one photosensitive drum 1 and an intermediate transfer belt 6 having a low back surface resistance, which is basically the same configuration as the image forming apparatus shown in FIG. 20. In the image forming apparatus, the bias from one power supply 15 is switched by switching the output polarity. First, a primary transfer is performed by applying a positive polarity voltage having a polarity opposite to the toner polarity to the primary transfer roller 14. A method of performing secondary transfer by switching the connection of the power supply 15 to apply a negative polarity voltage to the primary transfer roller 14 and the secondary transfer counter roller 11 and grounding the secondary transfer roller 7 is described. ing.

Japanese Patent Laid-Open No. 9-16001 JP 2001-228722 A

  As described above, there is disclosed a method of switching between primary transfer and secondary transfer with a single transfer power supply for cost reduction. However, with this method, since primary transfer cannot be performed during secondary transfer, image output cannot be performed efficiently.

  Therefore, in a full-color image forming apparatus having a single photosensitive drum, the primary transfer roller is reduced by not performing the primary transfer roller but also performing the primary transfer by supplying current from the secondary transfer roller to the intermediate transfer belt. Cost reduction can be realized. Further, the efficiency of image output can be improved by performing the primary transfer and the secondary transfer simultaneously.

  However, if only the current is supplied from the secondary transfer roller, the length of the intermediate transfer belt becomes longer than twice the maximum output image length. In order to further reduce the size of the apparatus, it is necessary to shorten the belt length.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to realize cost reduction and image output speed efficiency, and an image that can be reduced in size by shortening the peripheral length of the intermediate transfer member and omitting the intermediate transfer member cleaning device. A forming apparatus is provided.

  Image formation in which a toner image formed on an image carrier is transferred to an intermediate transfer member at a primary transfer portion, and the toner image transferred to the intermediate transfer member is transferred to a transfer material by a secondary transfer member at a secondary transfer portion. The apparatus includes a bias supply member that is connected to a secondary transfer power source that applies a voltage to the secondary transfer member, and that applies a bias voltage to the intermediate transfer member, and the intermediate transfer member moves in the moving direction from the primary transfer unit. The secondary transfer member and the bias supply member are sequentially arranged in the downstream direction, and when the maximum length of the transfer material that can be output by the image forming apparatus is M, the rotation direction of the intermediate transfer member is The intermediate transfer member outer peripheral surface distance DI from the primary transfer portion to the bias supply member is DI> M, and the intermediate transfer member outer peripheral surface distance SD from the secondary transfer member to the primary transfer portion is SD>. M, the via The intermediate transfer member outer peripheral surface distance IS from the supply member to the secondary transfer member is configured to satisfy IS> M, and when the peripheral length of the intermediate transfer member is L, L> 3M / 2 There is provided an image forming apparatus configured to transfer a toner image on the image carrier to the intermediate transfer member by applying a voltage to the secondary transfer member or the bias supply member. The

  Image formation in which a toner image formed on an image carrier is transferred to an intermediate transfer member at a primary transfer portion, and the toner image transferred to the intermediate transfer member is transferred to a transfer material by a secondary transfer member at a secondary transfer portion. The apparatus further comprises a charging member that applies a bias voltage to the intermediate transfer member, the toner reverse polarity charging member charging the secondary transfer residual toner on the intermediate transfer member to a polarity opposite to a normal toner polarity, The secondary transfer member and the toner reverse polarity charging member are sequentially arranged from the primary transfer portion toward the downstream side in the moving direction of the intermediate transfer member, and the maximum length of the transfer material that can be output by the image forming apparatus is set to M. The outer peripheral surface distance DI of the intermediate transfer member from the primary transfer portion to the toner reverse polarity charging member contact portion with respect to the rotation direction of the intermediate transfer member is DI> M, and from the secondary transfer portion to the first Intermediate to the next transfer section The intermediate outer peripheral surface distance IS from the toner reverse polarity charging member contact portion to the secondary transfer portion is IS> M, and the intermediate transfer surface distance SD is SD> M. A toner image on the image carrier is configured such that L> 3M / 2 when the circumference of the body is L, and a voltage is applied to the secondary transfer member or the toner reverse polarity charging member. Is transferred to the intermediate transfer member, and an image forming apparatus is provided.

  According to the present invention, the bias supply member that can be brought into contact with and separated from the intermediate transfer member is provided, and by optimizing the arrangement of the members around the intermediate transfer member, the rotation direction length (peripheral length) of the intermediate transfer member is shortened. The intermediate transfer member cleaning device can be omitted, and the device can be designed to be smaller.

1 is a schematic cross-sectional view illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 6 is a time-series operation schematic diagram of each component when one A4 full-color image is output according to the first exemplary embodiment of the present invention. It is a schematic sectional drawing explaining the circumferential direction resistance measuring method of the belt used for the intermediate transfer body of this invention. It is explanatory drawing explaining the circumferential direction resistance measurement result of the belt used for the intermediate transfer body of this invention. FIG. 2 is a schematic cross-sectional view showing an image forming apparatus having a transfer power source dedicated for primary transfer in each image forming unit. It is a time-sequential operation schematic diagram of each component at the time of continuous output of two A4 full-color images of Example 2 of the present invention. It is explanatory drawing explaining the effect of the constant voltage element of this invention. It is a schematic sectional drawing explaining the state which connected the Zener diode to each support member of Example 2 of this invention. It is a schematic sectional drawing explaining the state which connected the varistor to each support member of Example 2 of this invention. It is a schematic sectional drawing explaining the state which connected the shared Zener diode to the supporting member of Example 2 of this invention. It is a schematic sectional drawing explaining the state which connected the common varistor to the support member of Example 2 of this invention. It is a schematic sectional drawing which shows the image forming apparatus of another structure applicable to Example 2 of this invention. It is a schematic sectional drawing which shows the image forming apparatus which concerns on Example 3 of this invention. FIG. 10 is a time-series operation schematic diagram of each component during continuous output of two A4 full-color images according to Example 3 of the present invention. It is a schematic sectional drawing explaining the state which connected the varistor to each support member of Example 3 of this invention. It is a schematic sectional drawing explaining the state which connected the shared Zener diode to the supporting member of Example 3 of this invention. It is a schematic sectional drawing explaining the state which connected the common varistor to the support member of Example 3 of this invention. It is a schematic sectional drawing explaining the state which connected the shared resistive element to the supporting member of Example 3 of this invention. It is a schematic sectional drawing which shows the image forming apparatus of another structure applicable to Example 3 of this invention. It is the schematic showing the conventional image forming apparatus. It is the schematic showing the conventional image forming apparatus. It is the schematic showing the conventional image forming apparatus.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
An embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. However, the components described in this embodiment are merely examples, and the scope of the present invention is not limited to them.

  FIG. 1 is a schematic configuration diagram illustrating an example of an electrophotographic rotary full-color image forming apparatus 100 (one drum system) according to this embodiment. The maximum length that can be output by the image forming apparatus 100 of the present embodiment is an A4 vertical (297 mm) length.

  The image forming apparatus 100 includes a photosensitive drum 1 that sequentially forms toner images of respective colors, and a charging member 2, an exposure device 3, a developing device 4, and an image carrier cleaning device 5 that collects primary transfer residual toner are arranged around the periphery. Has been. Each developing device 4a, 4b, 4c, 4d contains yellow toner, magenta toner, cyan toner, and black toner, respectively.

  In this embodiment, the photosensitive drum 1 is a negatively charged organic photosensitive member, and has a photosensitive layer (not shown) on a drum base (not shown) such as aluminum, and a predetermined process speed by a driving device (not shown). Is driven to rotate.

  The charging member 2 contacts the photosensitive drum 1 with a predetermined pressure contact force, and uniformly charges the surface of the photosensitive drum 1 to a predetermined polarity and potential by a charging bias applied from a charging bias power source (not shown).

  The exposure device 3 outputs a laser beam modulated in accordance with a time-series electric digital pixel signal of image information inputted from a host computer (not shown) from a laser output unit (not shown), and the surface of the photosensitive drum 1. To expose. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1 (on the image carrier) charged by the charging member 2.

  The developing devices 4a, 4b, 4c, and 4d attach toner to the electrostatic latent image formed on the photosensitive drum 1 by the exposure device 3 and develop (visualize) the toner image.

Although not limited, the intermediate transfer member 6 is an endless belt in the present embodiment, and is stretched between a secondary transfer counter roller 11 and a tension roller 12 that also serve as a driving function (hereinafter referred to as these). The two rollers 11 and 12 are collectively referred to as a “stretching roller”). The intermediate transfer member 6 is rotated (moved) in the direction of the arrow (clockwise) by driving the secondary transfer counter roller 11 to which a motor (not shown) is connected. The secondary transfer counter roller 11 is provided with a high-friction rubber layer on the surface layer for driving the intermediate transfer member 6, and has a volume resistivity of 10 ⁵ Ω · cm or less. The secondary transfer counter roller 11 is in contact with the secondary transfer roller 7 (secondary transfer member) via the intermediate transfer body 6 to form a secondary transfer portion T2. The tension roller 12 is made of a metal roller, applies a tension of a total pressure of 60 N to the intermediate transfer body 6, and rotates following the intermediate transfer body 6. As will be described in detail later, a bias voltage supply member 10 for supplying a bias voltage to the intermediate transfer member 6 is disposed.

  The secondary transfer counter roller 11 and the tension roller 12 are grounded through one 1 GΩ resistor 30. Since the resistance of the rubber layer of the secondary transfer counter roller 11 is sufficiently smaller than 1 GΩ, the electrical influence can be ignored.

  In this embodiment, an image in which the primary transfer of the toner image from the photosensitive drum 1 to the intermediate transfer member 6 is performed by supplying current from the secondary transfer roller 7 to the intermediate transfer member 6 without using the primary transfer roller. Forming device. Therefore, special conditions are required for the length of the intermediate transfer member 6 and the positional relationship between the photosensitive drum 1, the secondary transfer roller 7, and the bias supply member 10. That is, when the length of the intermediate transfer member 6 and the positional relationship between the photosensitive drum 1, the secondary transfer roller 7, and the bias supply member 10 are not appropriate, the apparatus becomes larger, the already transferred toner image is disturbed, and the secondary transfer is performed. The problem of soiling the roller 7 occurs. In order to avoid such a problem, the length of the intermediate transfer member 6 and the positional relationship between the photosensitive drum 1 and the secondary transfer roller 7 and the bias supply member 10 which are sequentially arranged in the downstream direction of the intermediate transfer member movement are special. Conditions are required.

  Hereinafter, the length of the intermediate transfer member 6 and the positional relationship between the photosensitive drum 1, the secondary transfer roller 7, and the bias supply member 10 will be described.

  The bias supply member 10 is disposed downstream of the secondary transfer roller 7 in the rotational movement direction of the intermediate transfer body 6, and is a secondary transfer bias power source that is a secondary transfer power source that applies a voltage to the secondary transfer roller 7. 8 is also connected. The length of the intermediate transfer member 6 from the primary transfer portion T1 where the photosensitive drum 1 and the intermediate transfer member 6 are in contact to the contact portion of the bias supply member 10 (intermediate transfer member outer peripheral surface distance DI) needs to be the following length: It is. That is, the length is such that the primary transfer at the primary transfer portion T1 and the interference between the primary transferred toner image and the bias supply member 10 can be prevented. That is, in order to achieve both the primary transfer of the toner image on the photosensitive drum 1 onto the intermediate transfer member 6 and the prevention of interference between the toner image primarily transferred onto the intermediate transfer member 6 and the bias supply member 10. The A4 size of the transfer material P that can be output by the image forming apparatus 100 of the present embodiment needs to be longer than the length of 297 mm (maximum length M) (DI> M). In this embodiment, DI is set to 360 mm in consideration of the distance that the intermediate transfer member 6 moves between the contact / separation operation time of the bias supply member 10 and the rise time of the secondary transfer bias power supply 8. However, if the contact / separation operation time can be made shorter than that of the present embodiment, the length can be made shorter. The length of the intermediate transfer member 6 from the secondary transfer portion T2 to the primary transfer portion T1 in the downstream direction of the intermediate transfer member movement direction (intermediate transfer member outer peripheral surface distance SD) is also on the intermediate transfer member 6. In order to prevent interference between the transferred image and the secondary transfer roller 7, the length of the transfer material P that can be output needs to be longer (SD> M). In this embodiment, the length of the longest transfer material P that can be output is 297 mm in A4 size, and the intermediate transfer body 6 is between the contact / separation operation time of the secondary transfer roller 7 and the rise time of the secondary transfer bias power supply 8. SD = 360 mm in consideration of the distance traveled. Further, the length of the intermediate transfer body 6 (intermediate transfer body outer surface distance IS) from the contact portion of the bias supply member 10 to the secondary transfer portion T2 in the downstream direction of the intermediate transfer body movement direction is also 1 on the intermediate transfer body 6. In order to prevent interference between the next-transferred image and the secondary transfer roller 7 and the bias supply member 10, it is necessary to be longer than the length of the longest transfer material that can be output (IS> M). Therefore, IS = 380 mm is set for the same reason as described above. Therefore, the entire length of the intermediate transfer member 6 (peripheral length L = (DI + SD + IS) / 2, L> 3M / 2) is 550 mm in the image forming apparatus of this embodiment.

The secondary transfer roller 7 has an EPDM foam layer having a medium resistivity of 10 ⁷ to 10 ⁹ Ω · cm on the surface of the core metal (not shown) and a rubber hardness of 30 ° (Asker C hardness). It is configured to cover an elastic layer such as. Further, the secondary transfer roller 7 is pressed against the secondary transfer counter roller 11 through the intermediate transfer body 6 with a total pressure of about 39.2N. The secondary transfer roller 7 is driven to rotate as the intermediate transfer member 6 rotates. A secondary transfer bias power source (high voltage power source) 8 is connected to the secondary transfer roller 7.

  The bias supply member 10 uses the same roller as the secondary transfer roller 7, and is set to enter the intermediate transfer body 6 by 2 mm when contacting the intermediate transfer body 6. Further, as the intermediate transfer member 6 rotates, it is driven to rotate.

  Outside the intermediate transfer member 6, an intermediate transfer member cleaning device 9 that removes and collects secondary transfer residual toner remaining on the intermediate transfer member is disposed facing the tension roller 12.

  A fixing device 13 having a fixing roller 13a and a pressure roller 13b is installed on the downstream side in the transport direction of the transfer material P of the secondary transfer portion T2 where the secondary transfer counter roller 11 and the secondary transfer roller 7 abut. Yes.

  Next, an image forming operation by the above-described image forming apparatus will be described along with a case where one A4 full-color image is output.

  When an image forming operation start signal is issued, transfer materials (paper) P are sent out one by one from a cassette (not shown) and conveyed to a registration roller (not shown). At that time, the registration roller (not shown) is stopped, and the leading edge of the transfer material P stands by immediately before the secondary transfer portion T2.

On the other hand, when an image forming operation start signal is issued, the photosensitive drum 1 that is rotationally driven at a predetermined process speed is uniformly charged negatively by the charging member 2 in this embodiment. Then, the exposure apparatus 3 converts color-separated image signals input from a host computer (not shown) into optical signals by a laser output unit (not shown). Laser light, which is a converted optical signal, is scanned and exposed on the charged photosensitive drum 1 to sequentially form electrostatic latent images corresponding to the respective colors. The charge amount and exposure amount of the photosensitive drum 1 are adjusted so that the potential after being charged by the charging member 2 is −450 V and the potential (image portion) after being exposed by the exposure device 3 is −100 V. The developing bias is −300V. The process speed is 60 mm / sec. The image forming width, which is the length in the direction perpendicular to the transfer direction of the transfer material P (the rotation direction of the intermediate transfer belt), is 215 mm, the toner charge amount is −40 μC / g, and the toner amount on the photosensitive drum of the solid image portion is 0. It is set to 4 mg / cm ² .

  First, the first electrostatic color formed on the photosensitive drum 1 (hereinafter simply referred to as “first first color”) is charged with the charged polarity ( In this embodiment, yellow toner is attached by the developing device 4a to which a developing bias having the same polarity as that of the negative polarity is applied, and the toner image is visualized.

  From the secondary transfer bias power supply 8 to the bias supply member 10 (the state of the bias supply member 10a) that is in contact with the intermediate transfer member 6 by the contact / separation mechanism (not shown), the polarity (in the present embodiment, the polarity opposite to the toner polarity) )) Is applied. The current flows from the bias supply member 10 to the intermediate transfer member 6. Then, the yellow toner image is primarily transferred onto the rotating intermediate transfer member 6. In this embodiment, a voltage of 1.2 kV is supplied from the secondary transfer bias power supply 8, but this value is set to an optimum value depending on the paper or environment as the transfer material P.

  Hereinafter, a time-series operation of each component in the series of operations of the image forming apparatus 100 illustrated in FIG. 2 will be described.

  The bias application to the bias supply member 10 stops before the trailing edge of the yellow toner image passes through the primary transfer portion T1 and the leading edge of the yellow toner image reaches the bias supply member contact portion. At the same time, the bias supply member 10 is separated (the state of the bias supply member 10b) by the contact / separation mechanism. The transferred yellow toner image on the intermediate transfer body 6 passes through the bias supply member contact portion as the intermediate transfer body 6 moves. The secondary transfer roller 7 (secondary transfer roller) that has contacted the intermediate transfer body 6 by the contact / separation mechanism before the rear end of the yellow toner image has passed through the secondary transfer portion T2 and the leading end of the yellow toner image has reached the primary transfer portion T1. 7a), a bias is applied from the secondary transfer bias power source 8. After completion of the yellow toner image formation, the magenta toner developing device 4 b is moved to the opposite portion of the photosensitive drum 1 by the rotary rotation of the developing device 4. At the same time, the electrostatic latent image formed on the photosensitive drum 1 is developed with magenta toner which is the first and second color. The magenta toner image formed on the photosensitive drum 1 is superposed on the yellow toner image on the rotating intermediate transfer body 6 by the current from the secondary transfer roller 7 to start primary transfer.

  The rear end of the yellow toner image passes through the bias supply member contact portion, and the bias supply member 10 (bias supply) that contacts the intermediate transfer member 6 by the contact / separation mechanism before the front ends of the yellow and magenta toner images reach the secondary transfer portion T2. A bias is applied from the secondary transfer bias power supply 8 to the state of the member 10a. Immediately thereafter, the bias application to the secondary transfer roller 7 is stopped and the secondary transfer roller 7 is separated by the contact / separation mechanism (the state of the secondary transfer roller 7b). The yellow and magenta toner images pass through the secondary transfer portion T2 as the intermediate transfer member 6 moves. The rear end of the yellow and magenta toner images passes through the primary transfer portion T1, and the bias application to the bias supply member 10 stops before the front ends of the yellow and magenta toner images reach the bias supply member contact portion. At the same time, the bias supply member 10 is separated by the contact / separation mechanism (the state of the bias supply member 10b). The yellow and magenta toner images pass through the bias supply member contact portion as the intermediate transfer member 6 moves. The secondary transfer roller in which the rear end of the yellow and magenta toner images passes through the secondary transfer portion T2 and contacts the intermediate transfer body 6 by the contact / separation mechanism before the front ends of the yellow and magenta toner images reach the primary transfer portion T1. 7 (the state of the secondary transfer roller 7a) is applied with a bias from the secondary transfer bias power source 8. Next, the first and third cyan toner images formed on the photosensitive drum 1 are superimposed on the yellow and magenta toner images on the rotating intermediate transfer member 6 by the current from the secondary transfer roller 7. At the same time, the primary transfer is started.

  Bias supply in which the trailing edge of the yellow and magenta toner images passes through the bias supply member contact portion and contacts the intermediate transfer member 6 by the contact / separation mechanism before the leading edge of the yellow, magenta and cyan toner images reaches the secondary transfer portion T2. A bias is applied from the secondary transfer bias power supply 8 to the member 10 (bias supply member 10a). Immediately thereafter, the bias application to the secondary transfer roller 7 is stopped and the secondary transfer roller 7 is separated by the contact / separation mechanism (the state of the secondary transfer roller 7b). The yellow, magenta, and cyan toner images pass through the secondary transfer portion T2 as the intermediate transfer body 6 moves. The rear end of the yellow, magenta, and cyan toner images passes through the primary transfer portion T1, and the bias application to the bias supply member 10 stops before the front ends of the yellow, magenta, and cyan toner images reach the bias supply member contact portion. . At the same time, the bias supply member 10 is separated by the contact / separation mechanism (the state of the bias supply member 10b). The yellow, magenta, and cyan toner images pass through the bias supply member contact portion as the intermediate transfer member 6 moves. The rear end of the yellow, magenta, and cyan toner images passes through the secondary transfer portion T2, and the front end of the yellow, magenta, and cyan toner images comes into contact with the intermediate transfer body 6 by the contact / separation mechanism before reaching the primary transfer portion. A bias is applied from the secondary transfer bias power source 8 to the next transfer roller 7 (the state of the secondary transfer roller 7a). The black toner image of the first and fourth color formed next on the photosensitive drum 1 is yellow, magenta and cyan toner images on the rotating intermediate transfer member 6 by the current from the secondary transfer roller 7. The primary transfer is started in a superimposed manner.

  As the leading edges of the yellow, magenta, cyan, and black toner images reach the secondary transfer portion T2, the transfer material P is conveyed to the secondary transfer portion T2 by a registration roller (not shown). Then, a full-color toner image is secondarily transferred collectively onto the transfer material P by a secondary transfer roller 7 to which a bias is applied.

The intermediate transfer body cleaning device 9 is in contact with the intermediate transfer body 6 by the contact / separation mechanism (not shown) before the tip of the secondary transfer residual toner remaining on the intermediate transfer body 6 reaches the contact portion of the bias supply member. It becomes. As the intermediate transfer member 6 rotates, the secondary transfer residual toner that has reached the intermediate transfer member cleaning device 9 is collected. The transfer material P on which a full-color toner image has been formed is conveyed to the fixing device 13 and then the fixing roller 13a. The full-color toner image is heated and pressed at the fixing nip portion between the pressure roller 13b and the pressure roller 13b, thermally fixed on the surface of the transfer material P, and then discharged to the outside, thus completing a series of image forming operations.

  At the time of each primary transfer described above, the primary transfer residual toner remaining on the photosensitive drum 1 is removed and collected by the image carrier cleaning device 5.

  Here, the intermediate transfer member 6 used in the image forming apparatus 100 of the present embodiment will be described.

  Hereinafter, in the image forming apparatus 100 according to the present exemplary embodiment, a belt used for the intermediate transfer member 6 that is necessary for performing primary transfer of a toner image from the photosensitive drum 1 to the intermediate transfer member 6 without using a primary transfer roller. In order to explain these characteristics, the definition and measurement method of the circumferential resistance of the belt will be described.

  The belt used for the intermediate transfer member 6 of this example has a base layer in which carbon is dispersed in a polyphenylene sulfide (PPS) resin having a thickness of 100 μm to adjust electric resistance. The resins used are polyimide (PI), polyvinylidene fluoride (PVdF), nylon, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate, polyether ether ketone (PEEK), polyethylene naphthalate (PEN). ) Etc.

  Next, the manufacturing method of the base layer of a belt is demonstrated. In this embodiment, a manufacturing method using an inflation molding method is used. PPS serving as a base material and blending components such as carbon black as conductor powder are melt-kneaded by a biaxial kneader. An endless belt-like (endless belt) base layer is manufactured by extruding the obtained kneaded material with an annular die.

  In this embodiment, carbon black is used as the conductor powder. The additive to be mixed for adjusting the electric resistance value of the intermediate transfer member 6 is not particularly limited. For example, the conductive filler for adjusting the resistance includes carbon black and various conductive metal oxides. Non-filler resistance modifiers include low molecular weight ionic conductive materials such as various metal salts and glycols, antistatic resins containing ether bonds and hydroxyl groups in the molecule, or organic polymer compounds exhibiting electronic conductivity, etc. .

  When the amount of carbon to be added is increased, the resistance of the base layer belt is lowered. However, when the amount is excessively increased, the strength of the base layer belt itself is insufficient and the base belt is easily broken. In this embodiment, the resistance of the base layer belt is reduced so that the strength of the base layer belt can be used in the image forming apparatus.

  The Young's modulus of the belt of this example is about 3000 MPa. The Young's modulus measurement was based on the tensile modulus measurement method of JIS-K7127, and the thickness of the measurement sample was 100 μm.

  Table 1 shows belts in which the relative ratio of the carbon amount to the base layer is changed.

  Table 1 shows the amount of added carbon and the presence or absence of a surface coat layer. For example, belt B has a carbon amount 1.5 times that of belt A, and belt C has a carbon amount twice that of belt A. Further, the belt A, the belt B, and the belt C are provided with a surface layer, and the belt D and the belt E are single-layer belts. The relative ratio of the carbon amount of the belt B and the belt D is the same, and the relative ratio of the carbon amount of the belt C and the belt E is also the same.

  The surface coat layer is a high-resistance acrylic resin, and is formed by spray-coating an ultraviolet curable resin on the surface of the molded endless belt, drying, and curing by ultraviolet irradiation. If the coat layer is too thick, it tends to break, so the coating amount needs to be adjusted to be in the range of 0.5 to 3 μm.

Also, as a comparative belt, a polyimide comparative example belt having a resistance adjusted by changing the relative proportion of carbon amount was manufactured. The comparative belt has a relative carbon amount ratio of 0.5 and a volume resistivity of 10 ¹⁰ to 10 ¹¹ Ω · cm. The comparative belt is a belt having a general resistance value as a belt employed for the intermediate transfer member.

  In this embodiment, the resistance value of the belt whose resistance is lowered is measured by the method shown in FIG. A belt is stretched between two support members (electrically insulated), and a constant voltage (measurement voltage) is applied to the outer roller 21 (first metal roller) from a high-voltage power supply 20 that is a measurement power supply. At this time, the current flowing to the ammeter, which is current detection means connected to the outer roller 22 (second metal roller), is detected. From this detected current value, a method of obtaining the electric resistance of the belt between the position where the outer roller 21 contacts and the position where the outer roller 22 contacts is used. That is, by measuring the current flowing in the circumferential direction (rotating direction) of the belt by this method, the belt resistance is calculated by dividing the measurement voltage by the measured current value. At this time, in order to eliminate the influence of the resistance other than the belt, the outer rollers 21 and 22 are made of only metal (aluminum). In this embodiment, the distance from the outer roller 21 contact portion to the outer roller 22 contact portion is 275 mm on the belt upper surface side and 275 mm on the belt lower surface side.

  FIG. 4 shows the result of measuring the belts A to E by changing the applied voltage by the above measuring method. In this measurement method, the resistance in the circumferential direction, which is the rotational direction of the belt, is measured. Therefore, in this embodiment, the resistance of the intermediate transfer member 6 measured by this measuring method is referred to as circumferential resistance [Ω].

  As the applied voltage is increased for all belts, the resistance tends to decrease little by little. This is a characteristic of a belt in which carbon is dispersed in a resin.

  In the belts A to E, the resistance can be measured by the method shown in FIG. 3, but the resistance cannot be measured in the comparative belt. The comparative belt is a belt that is an intermediate transfer member 6 used in the image forming apparatus 100 having a configuration in which a voltage power source is connected to each of the primary transfer rollers 41, 42, 43, and 44 as shown in FIG. . The image forming apparatus 100 includes four image forming stations S (SY, SM, SC, SK) of yellow (Y), magenta (M), cyan (C), and black (K). Each image forming station S includes a photosensitive drum 1 (1a, 1b, 1c, 1d) and an exposure device 3 (3a, 3b, 3c, 3d) which are electrophotographic photosensitive members as an image carrier constituting an image forming unit. I have. Around each photosensitive drum 1, a charging roller 2 (2a, 2b, 2c, 2d) constituting a primary charging means as an image forming means, a developing means 4 (4a, 4b, 4c, 4d), an image carrier cleaning Means 5 (5a, 5b, 5c, 5d) is provided. The image forming apparatus 100 includes an intermediate transfer body 6, 41, 42, 43, 44 as primary transfer means, and a secondary transfer roller 7 as secondary transfer means, and 2 between the intermediate transfer body 6. A next transfer portion T2 is formed. The intermediate transfer member 6 has an endless belt shape, and is stretched by stretching members 10, 11, and 12 that are a driving roller, a secondary transfer counter roller, and a tension roller. When the image forming operation start signal is issued in the image forming apparatus 100, the surface of the photosensitive drum 1 is uniformly charged by the charging unit 2. In response to the image signal, the exposure unit 3 exposes the surface of the photosensitive drum 1 to form an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum 1 is developed into a toner image by the developing unit 4, and each color toner image is primarily transferred onto the intermediate transfer body 6. In order to primarily transfer the toner images of the respective colors onto the intermediate transfer body 6, primary transfer bias is applied to 41, 42, 43, and 44. Thereafter, the full-color toner image transferred as a superimposed image on the intermediate transfer body 6 is transferred onto the transfer material P by the secondary transfer means at the secondary transfer portion T2, and fixed by the fixing means 13.

  In such an image forming apparatus 100, the intermediate transfer body 6 is configured so that the four adjacent voltage power sources are not affected by currents flowing into each other via the intermediate transfer body 6 (so as not to interfere with each other). The volume resistance and surface resistance are designed to be high. That is, the comparative belt is a belt having a resistance that does not interfere with each primary transfer portion even when a voltage is applied to each primary transfer roller 41, 42, 43, 44, and current flows in the circumferential direction. Designed as a belt with difficult performance. A belt such as a comparative belt is defined as a high resistance belt, and a belt in which current flows in the circumferential direction such as belts A to E is defined as a conductive belt.

In this embodiment, the belt that can be used as the intermediate transfer member 6 is a conductive belt and has a circumferential resistance of 10 ⁴ Ω or more and 10 ⁸ Ω or less. Furthermore, in order to improve the secondary transfer property of small size paper, a multilayer structure having a high resistance coating layer on the outer surface of the base layer is preferable. This is to reduce the current difference between the sheet passing area and the non-sheet passing area in the longitudinal direction of the secondary transfer portion T2.

In the image forming apparatus 100 of this embodiment, when this belt is used, the circumferential resistance is low. Therefore, when current is supplied from the secondary transfer roller 7 or the bias supply member 10, the belt surface potential is substantially the same over the entire circumference. Become. In order to ensure primary transferability in the image forming apparatus 100 of this embodiment, a belt potential of 200 V or more is required. In the image forming apparatus 100 of the present embodiment, when high-quality paper (basis weight 75 g / m ² ) is used as the transfer material P, the secondary transfer voltage necessary for the secondary transfer is 1 kV or more. For example, in the image forming apparatus 100 of the present embodiment, when the output of the secondary transfer bias power supply 8 is always 1.2 kV, the belt potential is 200 V or more, and there is no problem in both primary transfer and secondary transfer. .

  With the configuration and operation as described above, image formation is excellent, toner contamination of the secondary transfer roller 7 and the bias supply member 10 is prevented, and the length of the intermediate transfer member 6 is shortened, so that the size of the apparatus can be reduced. It becomes.

Example 2
Next, a second embodiment will be described with reference to FIGS.

  The second embodiment is different from the first embodiment in that the secondary transfer is performed simultaneously with the primary transfer.

  That is, the image forming apparatus described with reference to FIG. 1 is also used in this embodiment. Accordingly, the description of the first embodiment is used, and details of the entire configuration of the image forming apparatus are omitted. Here, only a different part from Example 1 is demonstrated.

  In the first exemplary embodiment, the secondary transfer is not performed at the same time during the primary transfer, and the transfer material P is not present in the secondary transfer portion.

In the full-color image forming apparatus 100 of this embodiment using a belt having a circumferential resistance of 10 ⁴ Ω or more and 10 ⁸ Ω or less, each of the cases where A4 full-color images are continuously fed (when continuously output) FIG. 6 shows time-series operations of the constituent elements.

  During continuous printing, as shown by the shaded area in FIG. 6, the full-color image on the intermediate transfer member 6 is secondarily transferred to the transfer material P, and at the same time, the first color image of the next image is primarily transferred from the photosensitive drum 1 to the intermediate transfer member 6. May be transcribed.

  Here, the voltage applied to the secondary transfer roller 7 and the bias supply member 10 when only the primary transfer is performed, and the voltage applied to the secondary transfer roller 7 when the primary transfer and the secondary transfer are performed simultaneously, Both are 1.2 kV. By doing so, the belt potential is maintained at 200 V or more, and an output having no problem in both primary transfer and secondary transfer is possible.

  However, in the case where the transfer material P is present in the secondary transfer portion and in the case where the transfer material P is not present, since the overall resistance of the system changes, the flowing current changes and the belt potential changes accordingly. From this point of view, it is preferable that the belt potential does not change.

  Therefore, in the modified embodiment of this embodiment, the tension member is grounded via a constant voltage element having a threshold value instead of the 1 GΩ resistor element used in the first embodiment. This embodiment is shown in FIGS.

  FIG. 7 shows the relationship between the secondary transfer voltage and the belt potential when a constant voltage element (for example, a Zener diode or a varistor) is connected.

  The horizontal dotted line in FIG. 7 is a Zener potential or a varistor potential.

  FIG. 8 is a diagram illustrating a state in which a Zener diode is connected to each support member, and FIG. 9 is a diagram illustrating a state in which a varistor is connected to each support member.

  In the case of the resistor as used in Example 1, the belt potential also increased when the secondary transfer voltage was increased.

  However, in the case of a Zener diode or varistor as used in this embodiment, when the Zener potential or varistor potential is exceeded, a current flows through the constant voltage element, and the Zener potential or varistor potential is maintained. For this reason, even if the secondary transfer voltage is raised, the belt potential of the intermediate transfer member 6 does not rise above the Zener potential or the varistor potential. For this reason, the belt potential can be kept constant, and the primary transferability at the primary transfer portion T1 can be further stabilized. In addition, since the belt potential at the primary transfer portion T1 is constant even when the secondary transfer voltage is increased, the secondary transfer voltage that can be applied to the secondary transfer roller 7 has a wide setting range, and the secondary transfer voltage is set. The degree of freedom increases. Here, in this embodiment, the Zener potential or the varistor potential is set to 200v.

  With this configuration, the secondary transfer potential setting can be optimized independently of the primary transfer while stabilizing the primary transfer property. That is, since the surface potential of the intermediate transfer body 6 for primary transfer can be determined by the zener potential or varistor potential, the range of setting of the secondary transfer voltage is widened, and the applied bias for primary transfer and secondary transfer can be set. Can be optimized.

  In this way, by using a conductive belt-like intermediate transfer body 6, a Zener diode or varistor that maintains a predetermined potential is connected to each belt support member, and a voltage is applied from the secondary transfer bias power supply 8. The following becomes possible. That is, the surface potential of the intermediate transfer body 6 can be kept at a predetermined potential regardless of the presence or absence of the transfer material P or the change in resistance due to the presence of the transfer material, and the primary transfer and the secondary transfer are executed at the same timing. Is possible.

  In the above modified embodiment, a Zener diode, a varistor or the like is connected to each belt support member. However, as shown in FIGS. 10 and 11, common voltage elements such as a Zener diode and a varistor are connected to all the support rollers. It may be configured to do so. By sharing the constant voltage elements connected to the plurality of support rollers, the number of constant voltage elements can be reduced.

  Further, as shown in FIG. 12, in order to further stabilize the contact of the primary transfer portion, an electrically insulated primary transfer portion facing roller 51 may be provided.

Example 3
Next, a third embodiment will be described with reference to FIGS.

  In Example 3, the bias supply member 10 is changed to the toner reverse polarity charging member 61, the intermediate transfer member cleaning device 9 is eliminated, and the 1 GΩ resistance is changed to a Zener diode having a threshold of 200V. This is different from the first embodiment.

  Since most of the configuration of the image forming apparatus 100 of the present embodiment is the same as that of the first embodiment, the same components are denoted by the same reference numerals, the description of the first embodiment is used, and details thereof are omitted. Here, only a different part from Example 1 is demonstrated.

  FIG. 13 shows a schematic configuration diagram of the present embodiment. The maximum length that can be output by the image forming apparatus 100 of the present embodiment is an A4 vertical (297 mm) length.

  In the present embodiment, the toner reverse polarity charging member 61 serves both as the current supply function of the bias supply member 10 and the toner reverse polarity charging function in the first embodiment, and a contact / separation mechanism (not shown) with respect to the intermediate transfer body 6. And is connected to a high-voltage power source 62. That is, when there is no secondary transfer residual toner at the contact portion of the toner reverse polarity charging member 61 with the intermediate transfer member 6, it functions as a current supply member for primary transfer. When there is secondary transfer residual toner, it also functions to charge the secondary transfer residual toner to normal charging polarity (negative polarity) and reverse polarity (positive polarity).

  The secondary transfer residual toner generated on the intermediate transfer member 6 during image formation is charged to the reverse polarity by the toner reverse polarity charging member 61. Next, the secondary transfer residual toner charged to the reverse polarity on the intermediate transfer body 6 is carried to the primary transfer portion T1 as the intermediate transfer body 6 moves. At the primary transfer portion T2, the force of the primary transfer electric field (the surface potential of the intermediate transfer body 6 is the normal charge polarity of the toner (negative polarity in this embodiment) and the opposite polarity (positive polarity)) from the intermediate transfer body 6 Transferred to the photosensitive drum 1. Then, it is collected by the image carrier cleaning device 5. Therefore, in this embodiment, the intermediate transfer member cleaning device 9 in Embodiment 1 is not necessary.

In the present embodiment, although not limited, the toner reverse polarity charging member 61 is provided with a brush configured so that nylon fibers having a conductivity of 10 ⁶ to 10 ⁹ Ωcm are substantially dense. Using. The tip position of the toner reverse polarity charging member 61 is set so that the penetration amount is 1.0 mm with respect to the surface of the intermediate transfer member 6. The length of the toner reverse polarity charging member 61 in the longitudinal direction (direction intersecting the rotational movement direction of the intermediate transfer member 6) is substantially the same as the width of the image forming area on the intermediate transfer member 6 in the same direction. Thus, the toner reverse polarity charging member 61 rubs the surface of the intermediate transfer belt 6 as the intermediate transfer body 6 moves.

The intermediate transfer member 6 of this embodiment has an effect of improving the secondary transferability of small-size paper by reducing the current difference between the sheet passing area and the non-sheet passing area in the longitudinal direction of the secondary transfer portion T2. Therefore, in order to avoid interference between the intermediate transfer member potential and the toner reverse polarity charging member 61, a belt having a high resistance surface layer is used. Therefore, the belt used in this example has a high resistance surface layer and has a circumferential resistance of 10 ⁴ Ω or more and 10 ⁸ Ω or less.

  Next, an image forming operation performed by the image forming apparatus 100 according to the present exemplary embodiment will be described along an operation when two A4 size full-color images are continuously output.

  When an image forming operation start signal is issued, the transfer material P (paper) is sent out one by one from a cassette (not shown) and conveyed to a registration roller (not shown). At that time, the registration roller (not shown) is stopped, and the leading edge of the transfer material P stands by immediately before the secondary transfer portion T2.

On the other hand, when an image forming operation start signal is issued, the photosensitive drum 1 that is rotationally driven at a predetermined process speed is uniformly charged negatively by the charging member 2 in this embodiment. Then, the exposure apparatus 3 converts color-separated image signals input from a host computer (not shown) into optical signals by a laser output unit (not shown). Then, the exposure device 3 scans and exposes the laser beam, which is the converted optical signal, onto the photosensitive drum 1 charged by the charging member 2, and sequentially forms an electrostatic latent image corresponding to each color. The charge amount and exposure amount of the photosensitive drum 1 are adjusted so that the potential after being charged by the charging member 2 is −450 V and the potential (image portion) after being exposed by the exposure device 3 is −100 V. The developing bias is −300V. The process speed is 60 mm / sec. The image forming width which is the length in the direction perpendicular to the moving direction (rotating direction) of the photosensitive drum 1 is 215 mm, the toner charge amount is −40 μC / g, and the toner amount on the photosensitive drum 1 in the solid image portion is 0.4 mg / cm. It is set to be ² .

  FIG. 14 shows a time-series operation of each component in a series of operations when two sheets are continuously output.

  First, the yellow electrostatic latent image, which is the first color of the first sheet formed on the photosensitive drum 1, is applied with a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 1 by the developing device 4a. A toner is attached to make a visible image as a toner image.

  A reverse polarity charging bias (a polarity opposite to the toner (positive polarity)) from the high voltage power source 62 is applied to the toner reverse polarity charging member 61 (the state of the toner reverse polarity charging member 61a) in contact with the intermediate transfer body 6 by a contact / separation mechanism (not shown). ) Is applied. The yellow toner image is primarily transferred onto the rotating intermediate transfer member 6 by the current from the toner reverse polarity charging member 61.

  The bias application to the toner reverse polarity charging member 61 is stopped before the rear end of the yellow toner image passes through the primary transfer portion T1 and the front end of the yellow toner image reaches the toner reverse polarity charging member contact portion. At the same time, the toner reverse polarity charging member 61 is separated by the contact / separation mechanism (the state of the toner reverse polarity charging member 61b). The transferred yellow toner image on the intermediate transfer member 6 passes through the toner reverse polarity charging member contact portion as the intermediate transfer member 6 moves. The secondary transfer roller 7 (secondary transfer roller) that has contacted the intermediate transfer body 6 by the contact / separation mechanism before the rear end of the yellow toner image has passed through the secondary transfer portion T2 and the leading end of the yellow toner image has reached the primary transfer portion T1. The secondary transfer bias is applied from the secondary transfer bias power source 8 to the state 7a). After completion of the yellow toner image formation, the developing device 4 rotates to move the magenta toner developing device 4b to the opposite portion of the photosensitive drum 1, and the electrostatic latent image formed on the photosensitive drum 1 is the first sheet 2 Develop with colored magenta toner. The magenta toner image formed on the photosensitive drum 1 is superposed on the yellow toner image on the rotating intermediate transfer body 6 by the current from the secondary transfer roller 7 to start primary transfer.

  The toner reverse polarity charging member that has contacted the intermediate transfer member 6 by the contact / separation mechanism before the rear end of the yellow toner image passes through the toner reverse polarity charging member contact portion and before the yellow and magenta toner image front ends reach the secondary transfer portion T2. A reverse polarity charging bias is applied to 61 (the state of the toner reverse polarity charging member 61a) from a high voltage power source. Immediately thereafter, the bias application to the secondary transfer roller 7 is stopped and the secondary transfer roller 7 is separated by the contact / separation mechanism (the state of the secondary transfer roller 7b). The yellow and magenta toner images pass through the secondary transfer portion T2 as the intermediate transfer member 6 moves. The rear end of the yellow and magenta toner images passes through the primary transfer portion T1, and the bias application to the toner reverse polarity charging member 61 stops before the front ends of the yellow and magenta toner images reach the toner reverse polarity charging member contact portion. . At the same time, the toner reverse polarity charging member 61 is separated by the contact / separation mechanism (the state of the toner reverse polarity charging member 61b). The yellow and magenta toner images pass through the toner reverse polarity charging member contact portion as the intermediate transfer member 6 moves. The secondary transfer roller in which the rear end of the yellow and magenta toner images passes through the secondary transfer portion T2 and contacts the intermediate transfer body 6 by the contact / separation mechanism before the front ends of the yellow and magenta toner images reach the primary transfer portion T1. 7, the secondary transfer bias is applied from the secondary transfer bias power source 8. The cyan toner image of the first and third colors formed on the photosensitive drum 1 is superposed on the yellow and magenta toner images on the rotating intermediate transfer body 6 by the current from the secondary transfer roller 7 to be 1 Next transfer is started.

  The trailing edge of the yellow and magenta toner image passes through the toner reverse polarity charging member contact portion, and the leading edge of the yellow, magenta and cyan toner image contacts the intermediate transfer member 6 by the contact / separation mechanism before reaching the secondary transfer portion T2. A reverse polarity charging bias is applied to the toner reverse polarity charging member 61 from a high voltage power source. Immediately thereafter, the bias application to the secondary transfer roller 7 is stopped and the secondary transfer roller 7 is separated by the contact / separation mechanism (the state of the secondary transfer roller 7b). The yellow, magenta, and cyan toner images pass through the secondary transfer portion T2 as the intermediate transfer body 6 moves. The rear end of the yellow, magenta, and cyan toner images passes through the primary transfer portion T1, and the bias to the toner reverse polarity charging member 61 is reached before the front ends of the yellow, magenta, and cyan toner images reach the toner reverse polarity charging member contact portion. Application stops. At the same time, the toner reverse polarity charging member 61 is separated by the contact / separation mechanism (the state of the toner reverse polarity charging member 61b). The yellow, magenta, and cyan toner images pass through the bias supply member contact portion as the intermediate transfer member 6 moves. The trailing edge of the yellow, magenta, and cyan toner images passes through the secondary transfer portion T2, and the leading edge of the yellow, magenta, and cyan toner images contacts the intermediate transfer member 6 by the contact / separation mechanism before reaching the primary transfer portion T1. A secondary transfer bias is applied from the secondary transfer bias power source 8 to the secondary transfer roller 7 (the state of the secondary transfer roller 7a). The black toner image of the first and fourth colors formed on the photosensitive drum 1 is superimposed on the yellow, magenta, and cyan toner images on the rotating intermediate transfer body 6 by the current from the secondary transfer roller 7. Primary transfer is started.

  While the black toner image is primarily transferred, the transfer material P is transferred to the secondary transfer portion by a registration roller (not shown) in accordance with the leading edge of the yellow, magenta, cyan, and black toner images reaching the secondary transfer portion T2. Transport to T2. A full-color toner image is collectively transferred onto the transfer material P by a secondary transfer roller 7 to which a secondary transfer bias is applied.

  Before the leading edge of the secondary transfer residual toner remaining on the intermediate transfer member 6 reaches the toner reverse polarity charging member contact portion, the toner reverse polarity charging member 61 (toner reverse contact) that has contacted the intermediate transfer member 6 by the contact / separation mechanism. A reverse polarity charging bias is applied from the high voltage power source to the polarity charging member 61a. As the intermediate transfer member 6 rotates, the secondary transfer residual toner on the intermediate transfer member 6 is charged with a normal charging polarity (negative polarity) and a reverse polarity (positive polarity). The secondary transfer residual toner charged to the reverse polarity is conveyed to the primary transfer portion T1 as the intermediate transfer body 6 moves. In the primary transfer portion T1, the photosensitive drum 1 is transferred from the intermediate transfer body 6 with the force of the primary transfer electric field (the surface potential of the intermediate transfer body 6 is opposite to the normal charging polarity (negative polarity) of the toner (positive polarity)). And is collected by the image carrier cleaning device 5.

  During the secondary transfer of the first sheet, the primary transfer of the yellow toner image of the second sheet and the first color is started.

  After the formation of the first and fourth color black toner images on the photosensitive drum 1, the yellow toner image of the second and first color on the photosensitive drum 1 is started after T1 (= T2 + T3) sec. Here, T2sec is the time required for the secondary transfer residual trailing edge to move from the toner reverse polarity charging member contact portion to the primary transfer portion T1, and T3sec is after the secondary transfer residual trailing edge is transferred to the photosensitive drum 1. This is the time required for the bias application to the toner reverse polarity charging member to stop and enter the separated state.

  The reason why this time interval is required will be described next. After the first secondary transfer residual toner is completely transferred to the photosensitive drum 1, the bias application from the high voltage power source to the toner reverse polarity charging member 61 is stopped. Then, until the toner reverse polarity charging member 61 is separated (the toner reverse polarity charging member 61b) by the contact / separation mechanism, the leading edge of the second color first color image is prevented from reaching the toner reverse polarity charging member contact portion. Because. In other words, the toner reverse polarity charging member 61 remains in contact (the state of the toner reverse polarity charging member 61a) to prevent image disturbance and toner contamination of the toner reverse polarity charging member 61 due to the toner image coming in. .

  Immediately after the completion of the secondary transfer of the first sheet, the bias application to the secondary transfer roller 7 is stopped and the secondary transfer roller 7 is separated (the state of the secondary transfer roller 7b) by the contact / separation mechanism. . The yellow toner image passes through the secondary transfer portion T2 as the intermediate transfer member 6 moves. The trailing edge of the first secondary transfer residual toner reaches the primary transfer portion T1, the trailing edge of the second yellow toner image passes through the primary transfer portion T1, and the leading edge of the yellow toner image contacts the toner reverse polarity charging member. Bias application to the toner reverse polarity charging member 61 is stopped before reaching the portion. At the same time, the toner reverse polarity charging member 61 is separated by the contact / separation mechanism (the state of the toner reverse polarity charging member 61b). The yellow toner image passes through the bias supply member contact portion as the intermediate transfer member 6 moves. The secondary transfer roller 7 (secondary transfer roller) that has contacted the intermediate transfer body 6 by the contact / separation mechanism before the rear end of the yellow toner image has passed through the secondary transfer portion T2 and the leading end of the yellow toner image has reached the primary transfer portion T1. The secondary transfer bias is applied from the secondary transfer bias power source 8 to the state 7a). The second magenta toner image of the second color formed on the photosensitive drum 1 is superimposed on the yellow toner image on the rotating intermediate transfer body 6 by the current from the secondary transfer roller 7 to perform the primary transfer. Be started.

  The toner reverse polarity charging member 61 that contacts the intermediate transfer body 6 by the contact / separation mechanism before the rear end of the yellow toner image passes through the toner reverse polarity charging member contact portion and before the yellow and magenta toner image leading ends reach the secondary transfer portion. A reverse polarity charging bias is applied from a high voltage power source. Immediately thereafter, the application of bias to the secondary transfer roller 7 is stopped and the secondary transfer roller 7 is brought into a separated state (a state of the secondary transfer roller 7b) by the contact / separation mechanism. The yellow and magenta toner images pass through the secondary transfer portion T2 as the intermediate transfer member 6 moves. The rear end of the yellow and magenta toner images passes through the primary transfer portion T1, and the bias application to the toner reverse polarity charging member 61 stops before the front ends of the yellow and magenta toner images reach the toner reverse polarity charging member contact portion. . At the same time, the toner reverse polarity charging member 61 is separated by the contact / separation mechanism (the state of the toner reverse polarity charging member 61b). The yellow and magenta toner images pass through the toner reverse polarity charging member contact portion as the intermediate transfer member 6 moves. The secondary transfer roller in which the rear end of the yellow and magenta toner images passes through the secondary transfer portion T2 and contacts the intermediate transfer body 6 by the contact / separation mechanism before the front ends of the yellow and magenta toner images reach the primary transfer portion T1. A secondary transfer bias is applied from the secondary transfer bias power source 8 to the state 7 (the state of the secondary transfer roller 7a). The cyan toner image of the second and third colors formed on the photosensitive drum 1 is superposed on the yellow and magenta toner images on the rotating intermediate transfer member 6 by the current from the secondary transfer roller 7. Next transfer is started.

  The trailing edge of the yellow and magenta toner image passes through the toner reverse polarity charging member contact portion, and the leading edge of the yellow, magenta and cyan toner image contacts the intermediate transfer member 6 by the contact / separation mechanism before reaching the secondary transfer portion T2. A reverse polarity charging bias is applied from a high voltage power source to the toner reverse polarity charging member 61 (the state of the toner reverse polarity charging member 61a). Immediately thereafter, the bias application to the secondary transfer roller 7 is stopped and the secondary transfer roller 7 is separated by the contact / separation mechanism (the state of the secondary transfer roller 7b). The yellow, magenta, and cyan toner images pass through the secondary transfer portion T2 as the intermediate transfer body 6 moves. The rear end of the yellow, magenta, and cyan toner images passes through the primary transfer portion T1, and the bias to the toner reverse polarity charging member 61 is reached before the front ends of the yellow, magenta, and cyan toner images reach the toner reverse polarity charging member contact portion. Application stops. At the same time, the toner reverse polarity charging member 61 is separated by the contact / separation mechanism (the state of the toner reverse polarity charging member 61b). The yellow, magenta, and cyan toner images pass through the bias supply member contact portion as the intermediate transfer member 6 moves. The trailing edge of the yellow, magenta, and cyan toner images passes through the secondary transfer portion T2, and the leading edge of the yellow, magenta, and cyan toner images contacts the intermediate transfer member 6 by the contact / separation mechanism before reaching the primary transfer portion T1. A secondary transfer bias is applied from the secondary transfer bias power source 8 to the secondary transfer roller 7. The second and fourth black toner images formed on the photosensitive drum 1 are superimposed on the yellow, magenta, and cyan toner images on the rotating intermediate transfer member 6 by the current from the secondary transfer roller 7. Primary transfer is started.

  As the leading edge of the yellow, magenta, cyan, and black toner images reaches the secondary transfer portion T2, the transfer material P is conveyed to the secondary transfer portion T2 by a registration roller (not shown), and is transferred to the transfer material. Full-color toner images are secondarily transferred collectively by the secondary transfer roller 7 to which a secondary transfer bias is applied.

  Before the end of the secondary transfer residual toner remaining on the intermediate transfer body 6 reaches the toner reverse polarity charging member contact portion, the high pressure is applied to the toner reverse polarity charging member 61 that contacts the intermediate transfer body 6 by the contact / separation mechanism. A reverse polarity charging bias is applied from the power source. As the intermediate transfer member 6 rotates, the secondary transfer residual toner on the intermediate transfer member 6 is charged with a normal charging polarity (negative polarity) and a reverse polarity (positive polarity). The secondary transfer residual toner charged to the reverse polarity is conveyed to the primary transfer portion T1 as the intermediate transfer body 6 moves. In the primary transfer portion T1, the photosensitive drum 1 is transferred from the intermediate transfer body 6 with the force of the primary transfer electric field (the surface potential of the intermediate transfer body 6 is opposite to the normal charging polarity (negative polarity) of the toner (positive polarity)). And is collected by the image carrier cleaning device 5.

  The transfer material P on which the full-color toner image is formed is conveyed to the fixing device 13, and the full-color toner image is heated and pressed at the fixing nip portion between the fixing roller 13a and the pressure roller 13b to heat the surface of the transfer material P. After fixing, the sheet is discharged to the outside, and a series of image forming operations is completed.

  At the time of each primary transfer described above, the primary transfer residual toner remaining on the photosensitive drum 1 is removed and collected by the image carrier cleaning device 5.

In the image forming apparatus of this embodiment, when high-quality paper (basis weight 75 g / m ² ) is used as a transfer material, the secondary transfer voltage necessary for the secondary transfer is 1 kV or more. For example, in the image forming apparatus of the present embodiment, if the output of the secondary transfer bias power supply 8 is always 1.2 kV and the toner reverse polarity charging bias is 1 kV, the belt potential is 200 V, and both primary transfer and secondary transfer are problematic. There was no level.

  In this embodiment, a brush is used as the toner reverse polarity charging member 61. However, the present invention is not limited to this, and a roller, a combination of a brush and a roller, or the like may be used as long as the residual toner can be charged to a desired polarity. Good.

  In this embodiment, each tension member is grounded via a Zener diode, which is a constant voltage element, but an element such as a 1 GΩ resistance element or a varistor may be used instead of the Zener diode.

  FIG. 15 is a diagram illustrating a state in which the varistor is connected to each support member.

  Furthermore, as shown in FIGS. 16, 17, and 18, a configuration in which constant voltage elements such as Zener diodes and varistors and resistance elements, which are common to all the support rollers, are connected may be used. By sharing, it is possible to reduce the number of elements.

  In addition, as shown in FIG. 19, in order to further stabilize the contact of the primary transfer portion T1, an electrically insulated primary transfer portion facing roller 51 may be provided.

  In general, an image forming apparatus including a single photosensitive drum often has a single color mode as well as a full color mode. For example, in the black monochrome mode, it is not necessary to superimpose an image on the intermediate transfer body 6. For this reason, the black toner images sequentially formed on the photosensitive drum 1 are primarily transferred to the intermediate transfer body 6 sequentially, and the black toner images on the intermediate transfer body 6 are secondarily transferred to the transfer material P sequentially. During the image forming operation in the single color mode, the secondary transfer roller 7 and the toner reverse polarity charging member 61 are always brought into contact with the intermediate transfer body 6 to perform primary transfer, secondary transfer, secondary transfer residual toner photosensitive drum 1. The transfer to is performed sequentially.

1 Photosensitive drum (image carrier)
2 Charging member (charging means)
3 Exposure equipment (exposure means)
4 Developing device (Developing means)
DESCRIPTION OF SYMBOLS 5 Image carrier cleaning apparatus 6 Intermediate transfer body 7 Secondary transfer roller 8 Secondary transfer bias power supply 9 Intermediate transfer body cleaning apparatus 10 Bias supply member 11 Secondary transfer counter roller 12 Tension roller 20 High-voltage power supply 21 Outer roller 22 Outer roller 30 Resistance 41, 42, 43, 44 Primary transfer roller 51 Primary transfer portion opposing roller 61 Toner reverse polarity charging member 62 High voltage power supply 100 Image forming apparatus P Transfer material T1 Primary transfer portion T2 Secondary transfer

Claims (5)

Image formation in which a toner image formed on an image carrier is transferred to an intermediate transfer member at a primary transfer portion, and the toner image transferred to the intermediate transfer member is transferred to a transfer material by a secondary transfer member at a secondary transfer portion. In the device
A bias supply member connected to a secondary transfer power source for applying a voltage to the secondary transfer member and applying a bias voltage to the intermediate transfer member;
The secondary transfer member and the bias supply member are sequentially arranged from the primary transfer portion toward the downstream direction of the intermediate transfer member moving direction,
When the maximum length of the transfer material that can be output by the image forming apparatus is M, the outer peripheral surface distance of the intermediate transfer member from the primary transfer portion to the bias supply member with respect to the rotation direction of the intermediate transfer member DI is DI> M, the intermediate transfer member outer peripheral surface distance SD from the secondary transfer member to the primary transfer portion is SD> M, and the intermediate transfer member outer peripheral surface from the bias supply member to the secondary transfer member The distance IS is configured such that IS> M, and
When the peripheral length of the intermediate transfer member is L, L> 3M / 2,
An image forming apparatus, wherein a toner image on the image carrier is transferred to the intermediate transfer member by applying a voltage to the secondary transfer member or the bias supply member. Image formation in which a toner image formed on an image carrier is transferred to an intermediate transfer member at a primary transfer portion, and the toner image transferred to the intermediate transfer member is transferred to a transfer material by a secondary transfer member at a secondary transfer portion. In the device
A charging member that applies a bias voltage to the intermediate transfer member, and a toner reverse polarity charging member that charges secondary transfer residual toner on the intermediate transfer member to a polarity opposite to a normal toner polarity;
The secondary transfer member and the toner reverse polarity charging member are sequentially arranged from the primary transfer portion toward the downstream direction of the intermediate transfer member moving direction,
When the maximum length of the transfer material that can be output by the image forming apparatus is M, the outer periphery of the intermediate transfer member from the primary transfer portion to the toner reverse polarity charging member contact portion with respect to the rotation direction of the intermediate transfer member The surface distance DI is DI> M, the intermediate transfer member outer peripheral surface distance SD from the secondary transfer portion to the primary transfer portion is SD> M, and the toner reverse polarity charging member contact portion to the secondary transfer portion. The intermediate transfer member outer peripheral surface distance IS is configured such that IS> M,
When the peripheral length of the intermediate transfer member is L, L> 3M / 2,
An image forming apparatus, wherein a toner image on the image carrier is transferred to the intermediate transfer member by applying a voltage to the secondary transfer member or the toner reverse polarity charging member. A first metal roller to which a measurement voltage is applied from a measurement power source is brought into contact with the intermediate transfer member, and a second metal roller having a current detection means connected to the intermediate transfer member is connected to the first metal roller. The intermediate transfer member is contacted at a position distant in the rotation direction, and a value obtained by dividing the measurement voltage by the current value detected by the current detection unit is defined as a circumferential resistance of the intermediate transfer member, and the intermediate transfer member The image forming apparatus according to claim 1, wherein a value of the circumferential resistance of the body is 10 ⁴ Ω or more and 10 ⁸ Ω or less.   The image forming apparatus according to claim 1, wherein the intermediate transfer member has a multilayer structure, and a surface layer has a higher resistance than other layers.   The image forming apparatus according to claim 1, wherein a constant voltage element is connected to at least one of the plurality of support members.

Images