JP2005215189A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device by which transfer from a intermediate transfer belt to a recording material is successfully performed without occurrence of an image failure. <P>SOLUTION: In the image forming device with a photoconductive image carrier, a charging means for uniformly charging the image carrier, an exposure means for performing image exposure on the surface of the image carrier after charge to form an electrostatic latent image, a development means for making toner adhere to the electrostatic latent image to form a toner image, a first transfer means for transferring the toner image on the image carrier to an intermediate image carrier, a second transfer means which can be brought into contact with the intermediate image carrier for transferring the toner image on the intermediate image carrier to the recording material and having a fixing member for conveying the recording material to which the toner image on the intermediate image carrier is transferred to the fixing member and fixing the toner image on the recording material by sandwiching the recording material, the development means is constituted of five or more developing devices and charge amount of toner sequentially becomes high in order of transfer processes by the first transfer means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus used in, for example, a copying machine, a printer, a facsimile machine, a plate making system, and the like.

  As high-speed, high-quality image forming apparatuses, copying machines and laser beam printers that employ an electrophotographic method are known. Due to recent advances in digital technology, the demand for higher image quality of the electrophotographic image recording apparatus has increased from the POD market to the consumer market for offices and homes. In addition to images subjected to screen processing such as printing, There is an increasing demand for image characteristics having very high gradation like silver halide photography, having a wide color reproduction range and good graininess. In particular, with the rapid spread of CG images and digital cameras, it is desired to realize a wide color reproduction range approaching that of a silver salt photograph.

  In this electrophotographic image recording apparatus, an image carrier is irradiated with light by a laser beam or the like, and an image is recorded according to the amount of light irradiated at that time. Any image up to an image including a halftone can be formed. When reproducing the intermediate density at this time, various patterns can be formed on the image carrier by using a pulse width modulation method (PWM method) and an image processing method such as a dither method or a density pattern method. it can.

  Charged toner particles are attached to the pattern on the obtained image carrier, and further transferred and fixed on paper to obtain a final output image. As toner particles used at this time, four colors of yellow, magenta, cyan, and black are generally used for improving various image characteristics such as graininess, gradation, density, saturation, and gloss. Various improvements have been made.

  FIG. 9 is a schematic diagram for explaining a conventional example using four colors of yellow, magenta, cyan, and black (see, for example, Patent Document 1).

  An intermediate transfer belt 51 ', which is an endless intermediate image carrier that runs in the direction of arrow A', is disposed in the image forming apparatus main body. The intermediate transfer belt 51 'is made of a conductive or dielectric resin such as polycarbonate, polyethylene terephthalate resin film, polyvinylidene fluoride resin film, or the like. The recording material P ′ taken out from the paper feed cassette 8 ′ is supplied to the secondary transfer section through the registration roller 82 ′, and further conveyed to the left in FIG.

  Above the intermediate transfer belt 51 ', four image forming portions Pa', Pb ', Pc', Pd 'having substantially the same configuration are arranged in series. The configuration of the image forming unit Pa ′ will be described as an example.

  The image forming portion Pa 'includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 1a' that is rotatably arranged. Around the photosensitive drum 1a ', process devices such as a primary charger 2a' and a developing device 4a 'are arranged. The other image forming units Pb ′, Pc ′, and Pd ′ have the same configuration as the image forming unit Pa ′, and only the photosensitive drums 1b ′, 1c ′, and 1d ′ are illustrated in FIG. is there. The image forming units 1a ', 1b', 1c ', and 1d' are different in that toner images of respective colors of yellow, magenta, cyan, and black are formed.

  It is assumed that yellow toner, magenta toner, cyan toner, and black toner are stored in the developing devices disposed in the respective image forming units.

  An image signal based on the magenta component color of the document is projected onto the photosensitive drum 1a ′ via a polygon mirror (not shown) or the like to form an electrostatic latent image, and yellow toner is supplied from the developing device to the electrostatic latent image. The image becomes a yellow toner image. When the toner image arrives at a transfer portion where the photosensitive drum 1a ′ and the intermediate transfer belt 51 ′ come into contact with the rotation of the photosensitive drum 1a ′, the first transfer bias applied by the first transfer member 53a ′. Thus, the yellow toner image is transferred to the intermediate transfer belt 51 ′. When the intermediate transfer belt 51 ′ carrying the yellow toner image is conveyed to the image forming unit Pb ′, it has been formed on the photosensitive drum 1 b ′ by the same method as described above in the image forming unit Pb ′. The magenta toner image is transferred onto the yellow toner image.

  Similarly, as the recording material P ′ advances to the image forming portions Pc ′ and Pd ′, the cyan toner image and the black toner image are superimposed and transferred to the above-described toner image at each transfer portion, and until this time. Further, the recording material P ′ taken out from the paper feeding cassette 8 ′ once stops the leading end of the registration roller portion 82 ′, and the image formed on the intermediate transfer belt 51 ′ is transferred to a predetermined position of the recording material. Adjust the timing as required. The recording material P ′ fed from the registration roller 82 ′ at a predetermined timing reaches the second transfer portion 58 ′, and the above-mentioned four color toners are transferred by the transfer bias applied to the second transfer member 57 ′. The image is transferred onto the recording material P ′.

  The recording material P ′ is conveyed from the second transfer unit 58 ′ to the fixing unit 7 ′. The fixing unit 7 ′ has a step of fixing the toner onto the recording material P ′ by heat and pressure. Further, in order to improve the releasability between the recording material P ′ and the fixing roller 71 ′, it has a mechanism for coating the surface of the fixing roller 71 ′ with a releasable oil (for example, silicone oil). This oil also adheres to P ′. The recording material P ′ on which the toner image is fixed is discharged to a discharge tray (not shown). In the case of automatically forming a double-sided image, the image can be formed on the back surface by passing through a recording material reversing path (not shown) and repeating the above-described series of image forming processes.

  Further, for the purpose of further improving the image quality, a plurality of toners having different density levels are used as in Patent Documents 1 to 6, and further improvement in graininess and gradation reproducibility are performed from the highlight to the halftone area. Techniques for realizing improvements and the like are disclosed.

  FIG. 8 is a schematic diagram for explaining a conventional example using six colors of light magenta and light cyan in addition to yellow, magenta, cyan and black.

  An intermediate transfer belt 51 that is an endless intermediate image carrier that travels in the direction of arrow A is disposed in the image forming apparatus main body. The intermediate transfer belt 51 is made of a conductive or dielectric resin such as polycarbonate, polyethylene terephthalate resin film, polyvinylidene fluoride resin film, or the like. The recording material P taken out from the paper feed cassette 8 is supplied to the secondary transfer section through the registration roller 82 and further conveyed leftward in the figure.

  Above the intermediate transfer belt 51, six image forming portions Pa, Pb, Pc, Pd, Pe, and Pf having substantially the same configuration are arranged in series. The configuration of the image forming unit Pa will be described as an example.

  The image forming section Pa includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 a that is rotatably arranged. Around the photosensitive drum 1a, process devices such as a primary charger 2a and a developing device 4a are arranged. The other image forming units Pb, Pc, and Pd have the same configuration as that of the image forming unit Pa, and only the photosensitive drums 1b, 1c, 1d, 1e, and 1f are illustrated in FIG. The image forming units 1a, 1b, 1c, 1d, 1e, and 1f are different in that toner images of respective colors of yellow, magenta, light magenta, cyan, light cyan, and black are formed.

  It is assumed that yellow toner, magenta toner, light magenta toner, cyan toner, light cyan toner, and black toner are stored in the developing units disposed in the respective image forming units.

  An image signal based on the magenta component color of the document is projected onto the photosensitive drum 1a via a polygon mirror (not shown) or the like to form an electrostatic latent image, and yellow toner is supplied from the developing device to the electrostatic latent image. Becomes a yellow toner image. When this toner image arrives at the transfer portion where the photosensitive drum 1a and the intermediate transfer belt 51 come into contact with the rotation of the photosensitive drum 1a, the yellow toner is applied by the first transfer bias applied by the first transfer member 53a. The toner image is transferred to the intermediate transfer belt 51. When the intermediate transfer belt 51 carrying the yellow toner image is conveyed to the image forming portion Pb, the magenta toner image formed on the photosensitive drum 1b in the image forming portion Pb by the same method as described above. Is transferred onto the yellow toner image.

  Similarly, as the recording material P advances to the image forming portions Pc and Pd, the cyan toner image and the black toner image are superimposed and transferred onto the above-described toner images at the respective transfer sites, and by this time, the recording material P is supplied. The recording material P taken out from the paper cassette 8 once stops the leading end of the registration roller unit 82, and the timing is adjusted so that the image formed on the intermediate transfer belt 51 is transferred to a predetermined position of the recording material. . The recording material P fed from the registration roller 82 at a predetermined timing reaches the second transfer portion 58, and the above four color toner images are recorded by the transfer bias applied to the second transfer member 57. Transferred onto P.

  The recording material P is conveyed from the second transfer unit 58 to the fixing unit 7. The fixing unit 7 has a step of fixing the toner onto the recording material by heat and pressure. Further, in order to improve the releasability between the recording material P and the fixing roller 71, a mechanism for coating the surface of the fixing roller 71 with releasable oil (for example, silicone oil) is provided on the recording material P. Also this oil adheres. The recording material P on which the toner image is fixed is discharged to a discharge tray (not shown). When the double-sided image is automatically formed, the image can be formed on the back side by passing through a recording material reversal path (not shown) and repeating the above-described series of image formation processes.

JP-A-5-35038 JP-A-8-171252 JP 2000-231279 A JP 2000-305339 A JP 2000-347476 A JP 2001-290319 A JP 2002-091121 A

  Conventionally, in the four-color image forming apparatus shown in FIG. 9, the charge amounts of toner composed of yellow, magenta, cyan, and black formed on the photosensitive drum 1 ′ are substantially equal, and are applied to the transfer member 53 ′. The transfer bias is set to the same current or voltage. When the yellow toner image formed on the photosensitive drum 1a ′ positioned at the most upstream in the rotation direction of the intermediate transfer belt 51 ′ is transferred onto the intermediate transfer belt 51 ′ by the first transfer bias applied to the transfer member 53a ′. The toner charge amount on the photosensitive drum 1a ′ is an average of 25 μC / g as indicated by α in FIG. 10, whereas the first transfer bias applied to the transfer member 53a ′ and the photosensitive drum 1a. As a result of the peeling discharge generated at the time of separation after the end of the transfer process between “and the intermediate transfer belt 51”, an average of 30 μC / g was shifted to the high charge amount side as indicated by β in FIG. 10. Thereafter, the first transfer bias and the peeling discharge applied to the transfer members 53b ′, 53c ′, and 53d ′ are sequentially shifted to γ, δ, and ε in FIG. Immediately before the transfer portion 58 ′, the charge amount was ε as shown in FIG. Similarly, the magenta toner has a charge amount shown in FIG. 10, the cyan toner has a charge amount shown in FIG. 10, and the black toner has a charge amount shown in FIG.

  At this time, the second transfer portion 58 ′ must transfer toner having a charge amount from β to ε in FIG. 10, but the transfer process has a distribution of about ± 10 μC / g (A in FIG. 10). If it is present, the image can be transferred without any problem, and no image defect occurs even when the image is transferred to the recording material P ′ at the second transfer portion 58 ′ (B in FIG. 10).

  However, as shown in FIG. 2, in a six-color image forming apparatus to which light magenta and light cyan are further added in order to obtain a higher quality image, a maximum of six transfer steps are performed before the second transfer. Therefore, as shown in FIG. 11, the charge amount of the toner is η ′ in FIG. 11 for yellow toner, ζ ′ in FIG. 11 for magenta toner, ε ′ in light magenta toner, and cyan toner in FIG. The amount of charge on the drum (α ′ in FIG. 11) changed from δ ′, light cyan toner to γ ′ in FIG. 11, and black toner to β ′ in FIG.

  Therefore, in the second transfer portion 58, when the transfer bias applied to the second transfer member 57 is set to B ′ in FIG. 11, toner that is shifted to the high charge amount side, particularly yellow toner and magenta toner. As a result, it was impossible to give the charge necessary for sufficiently transferring the recording material P to the recording material P, resulting in a transfer failure (hereinafter, this phenomenon is referred to as weak omission). In addition, when the transfer bias applied to the transfer member 57 is set to D ′ in FIG. 11, an excessive charge is supplied to transfer toner on the low charge amount side, particularly light cyan toner and black toner, The charging polarity of the toner is reversed, and a transfer failure (hereinafter, this phenomenon is referred to as “strong omission”) that returns to the intermediate transfer belt 51 has occurred. Furthermore, when the transfer bias is set to C ′ in FIG. 11 so as to be in the middle, both transfer defects occurred in which yellow toner was weakly lost and black toner was strongly lost.

  Accordingly, the object of the present invention is to transfer from the intermediate transfer belt to the recording material by sequentially increasing the charge amount of the toner image formed on the photosensitive drum according to the number of transfer processes. It is an object of the present invention to provide an image forming apparatus that can be satisfactorily performed without causing image defects.

  Here, the toner charge amount used was an espert analyzer manufactured by Hosokawa Micron Corporation.

  To achieve the above object, the present invention provides a photoconductive image carrier, charging means for uniformly charging the image carrier, and image exposure of the charged image carrier surface to form an electrostatic latent image. An exposure means for developing, a developing means for forming a toner image by attaching toner to the electrostatic latent image, a first transfer means for transferring the toner image on the image carrier to the intermediate image carrier, Second transfer means capable of contacting an intermediate image carrier for transferring a toner image on the image carrier to a recording material, and the recording material onto which the toner image on the intermediate image carrier is transferred as a fixing member In the image forming apparatus having the fixing member that conveys and fixes the toner image on the recording material by sandwiching the recording material, the developing means is composed of five or more developing devices, and the first transfer means The charge amount of toner is sequentially increased in the order of the transfer process by

  According to the present invention, a photoconductive image carrier, a charging unit that uniformly charges the image carrier, an exposure unit that forms an electrostatic latent image by image exposing the surface of the image carrier after charging, At least one of light yellow, light magenta, light cyan, light black, red, green, blue, white, and transparent is formed by attaching toner to the electrostatic latent image to form a toner image. Developing means using color, first transfer means for transferring the toner image on the image carrier to the intermediate image carrier, and intermediate image carrier for transferring the toner image on the intermediate image carrier to the recording material A second transfer means capable of contacting the body, transporting the recording material onto which the toner image on the intermediate image carrier has been transferred to a fixing member, and sandwiching the recording material on the recording material Image shape having fixing member to be fixed In the apparatus, the developing means is composed of five or more developing apparatuses, and by setting the toner charge amount sequentially higher in the order of the transfer process by the first transfer means, it is possible to obtain a good image with no transfer failure. did it.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
Embodiment 1 of the present invention will be described with reference to a schematic cross-sectional view of an image forming apparatus in FIG.

  In FIG. 8, an endless intermediate transfer belt 51 running in the direction of arrow A is disposed in the image forming apparatus main body. The intermediate transfer belt 51 employs conductive polyimide in the present embodiment. The recording material P taken out from the paper feed cassette 8 is supplied to the secondary transfer unit 58 through the registration roller 82 and further conveyed to the left in the figure.

  Above the intermediate transfer belt 51, six image forming portions Pa, Pb, Pc, Pd, Pe, and Pf having substantially the same configuration are arranged in series. The configuration of the image forming unit Pa will be described as an example.

  The image forming section Pa includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 a that is rotatably arranged. Around the photosensitive drum 1a, process devices such as a primary charger 2a and a developing device 4a are arranged. The other image forming portions Pb, Pc, Pd, Pe, and Pf have the same configuration as that of the image forming portion Pa, and only the photosensitive drums 1b, 1c, 1d, 1e, and 1f are illustrated in FIG. It is. The image forming units 1a, 1b, 1c, 1d, 1e, and 1f are different in that toner images of respective colors of yellow, magenta, light magenta, cyan, light cyan, and black are formed.

  It is assumed that yellow toner, magenta toner, light magenta toner, cyan toner, light cyan toner, and black toner are stored in the developing devices disposed in the respective image forming units.

  An image signal based on the yellow component color of the document is projected onto the photosensitive drum 1a via a polygon mirror (not shown) or the like to form an electrostatic latent image, and yellow toner is supplied from the developing device to the electrostatic latent image. Becomes a yellow toner image. When this toner image arrives at the transfer portion where the photosensitive drum 1a and the intermediate transfer belt 51 come into contact with the rotation of the photosensitive drum 1a, the yellow toner is applied by the primary transfer bias applied by the primary transfer roller 53a. The image is transferred to the intermediate transfer belt 51. When the intermediate transfer belt 51 carrying the yellow toner image is conveyed to the image forming portion Pb, the magenta toner image formed on the photosensitive drum 1b in the image forming portion Pb by the same method as described above is obtained. Transferred onto the yellow toner image.

  Similarly, as the recording material P advances to the image forming portions Pc and Pd, the light magenta toner image, the cyan toner image, the light cyan toner image, and the black toner image are superimposed and transferred onto the above-described toner images at the respective transfer portions. Thereafter, until this time, the recording material P taken out from the paper feed cassette 8 reaches the secondary transfer portion 58, and the above four color toner images are recorded on the recording material P by the transfer bias applied to the secondary transfer roller 57. Transcribed above.

  The recording material P is conveyed from the second transfer unit 58 to the fixing unit 7. The fixing unit 7 has a step of fixing the toner onto the recording material by heat and pressure. Further, in order to improve the releasability between the recording material P and the fixing roller 71, it has a mechanism for coating the surface of the fixing roller with releasable oil (for example, silicone oil). This oil adheres. The recording material P on which the toner image is fixed is discharged to a discharge tray. When the double-sided image is automatically formed, the image can be formed on the back side by passing through a recording material reversal path (not shown) and repeating the above-described series of image formation processes.

  The conveyance speed of the recording material P in the fixing unit 78 is smaller than the conveyance speed of the secondary transfer unit 58. This is to prevent a shock image in which the image of the secondary transfer portion is disturbed by a shock when the recording material enters the fixing portion 78, or to prevent wrinkles of the recording material P generated in the fixing portion 78.

In such an image forming apparatus, in the present embodiment, carbon black is dispersed as the intermediate transfer belt 51 to obtain a surface resistivity of 109.
A semiconductive polyimide belt whose resistance is controlled to Ω / □ to 1014 Ω / □ is employed. The secondary transfer roller 57 employs a sponge roller made of ionic conductive nitrile butadiene rubber whose resistance is adjusted to a volume resistivity of 105 Ω · cm to 109 Ω · cm.

  The secondary transfer roller 57 is configured to abut on the upstream position in the transport direction of the intermediate transfer belt 51 from where the opposing roller 56 contacts the intermediate transfer belt 51. This is effective for abnormal discharge images generated on the upstream side of the secondary transfer portion 58, scattering of fine lines and characters, and is effective for peeling the recording material P from the intermediate transfer belt 51.

  Next, in this embodiment, the average charge amount of the yellow toner stored in the developing device 4a is approximately −20 μC / g (DY in FIG. 2) on the photosensitive drum 1a as shown in FIG. Thereafter, in the primary transfer processes of magenta, light magenta, cyan, light cyan, and black, they change to Y1, Y2, Y3, Y4, and Y5 of FIG. 2, respectively, and PY of FIG. 2 and −50 μC / g immediately before the secondary transfer process. It is trying to become. This charge amount needs to be adjusted so as to be appropriate depending on the configuration of the image forming apparatus and the material of the toner. The high pressure condition applied to the primary transfer roller 53 is constant current control of +15 μA (53a), +18 μA (53b), +21 μA (53c), +24 μA (53d), +27 μA (53e), and +30 μA (53f). . This control may be constant voltage control adjusted so that a desired current flows.

  Similarly, magenta is DM → M1 → M2 → M3 → M4 → PM, light magenta is DLM → LM1 → LM2 → LM3 → PLM, and cyan is FIG. 5 as shown in FIG. As shown in FIG. 4, DC → C1 → C2 → PC, light cyan is DLC → LC1 → PLC, and black is DK → PK, respectively, 25 μC / g, −30 μC / g, −35 μC / g, −40 μC / g. , And is set to increase sequentially from −45 μC / g to −50 μC / g.

  FIG. 1 shows the charge amount of the toner on these photosensitive drums. In accordance with the transfer process, yellow, magenta, light magenta, cyan, light cyan, and black are set to increase in this order, and the secondary transfer process. Then, all colors are set to have the same charge amount.

  As a result, a voltage suitable for transfer onto the recording material P can be applied to the secondary transfer roller 57, and a good image free from transfer defects such as strong omission and weak omission could be obtained. Here, the constant voltage control is adjusted so that a current of −135 μA is applied to the secondary transfer roller 57. This high voltage condition may be constant current control.

  Furthermore, it goes without saying that it is effective as a means of realizing light image quality comparable to silver salt by adding light yellow or light black.

  In addition to yellow, magenta, cyan, and black, more faithful color reproducibility can be realized by using red, green, and blue.

<Embodiment 2>
In the present embodiment, while the first embodiment is a tandem type, the case of a six-color rotary developing device will be described with reference to FIG.

  In FIG. 12, an endless intermediate transfer belt 51 running in the direction of arrow A is disposed in the image forming apparatus main body. The intermediate transfer belt 51 employs conductive polyimide in the present embodiment. The recording material P taken out from the paper feed cassette 8 is supplied to the secondary transfer unit 58 through the registration roller 82 and further conveyed to the left in the figure.

  Above the intermediate transfer belt 51, there is provided a drum-shaped electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 1a rotatably arranged. Around the photosensitive drum 1a, process devices such as a primary charger 2a and a developing device 4 are arranged. Six developing units 4a, 4b, 4c, 4d, 4e, 4f having substantially the same configuration are arranged in the rotary developing unit 4, and the desired developing unit is opposed to the photosensitive drum 1 by rotating to perform image formation. Is called. Here, the configuration will be described taking yellow image formation as an example. The differences between the developing devices 4a, 4b, 4c, 4d, 4e, and 4f are that toner images of respective colors of yellow, magenta, light magenta, cyan, light cyan, and black are formed.

  A photosensitive drum 1 that runs in the direction of the arrow is disposed in the image forming apparatus main body. The recording material P taken out from the paper feed cassette 8 is supplied to the batch transfer unit 58 via the registration roller 82 and further conveyed to the left in the figure.

  An image signal based on the yellow component color of the document is projected onto the photosensitive drum 1 through the polygon mirror 9a and the like to form an electrostatic latent image. In synchronization with this, the yellow developing device 4a is positioned at a position facing the photosensitive drum 1. Thus, the rotary developing device 4 rotates and yellow toner is supplied from the yellow developing device 4a, so that the electrostatic latent image becomes a yellow toner image. When the toner image arrives at a transfer portion where the photosensitive drum 1 and the intermediate transfer belt 51 come into contact with the rotation of the photosensitive drum 1, the yellow toner image is applied by the primary transfer bias applied by the primary transfer roller 53. Is transferred to the intermediate transfer belt 51. The intermediate transfer belt 51 carrying the yellow toner image rotates in preparation for the next transfer of magenta toner.

  Next, the toner remaining on the photosensitive drum 1 after the completion of the primary transfer is removed from the surface of the photosensitive drum 1 by the cleaning device 6, and the residual charge is removed by a charge removal device (not shown) such as a pre-exposure lamp. In preparation for the next image formation. The magenta toner image formed on the photosensitive drum 1 by the same method as described above is transferred onto the yellow toner image on the intermediate transfer belt 51.

  Similarly, after the recording material P is superimposed and transferred onto the above-mentioned toner image, the recording material P taken out from the paper feed cassette 8 after the light magenta toner image, cyan toner image, light cyan toner image, and black toner image are transferred. The four color toner images are transferred onto the recording material P by the transfer bias applied to the secondary transfer roller 57 after reaching the secondary transfer portion 58.

  The recording material P is conveyed from the second transfer unit 58 to the fixing unit 7. The fixing unit 7 has a step of fixing the toner onto the recording material by heat and pressure. Further, in order to improve the releasability between the recording material P and the fixing roller 71, it has a mechanism for coating the surface of the fixing roller with releasable oil (for example, silicone oil). This oil adheres. The recording material P on which the toner image is fixed is discharged to a discharge tray. When a double-sided image is automatically formed, an image can be formed on the back side by passing through a recording material reversal path (not shown) and repeating the above-described series of image formation processes.

  It goes without saying that the same effect as in the first embodiment can be obtained also in the transfer section by sequentially increasing the charge amount of the toner of each color in such an image forming apparatus.

  In this embodiment, an image forming apparatus in which six color developing units are arranged on a rotary on one photosensitive drum is used. However, three color developing units are arranged on two rotarys on two photosensitive drums, respectively. However, the same effect can be obtained.

<Embodiment 3>
In this embodiment, white toner and transparent toner are used in place of the light cyan toner and light magenta toner in the first or second embodiment, and the order of the transfer process is yellow (Pa), magenta (Pb), cyan (Pc). ), Black (Pd), white (Pe), and transparent (Pf) are the same as those in the first or second embodiment, and the description thereof will be omitted.

<Embodiment 4>
In this embodiment, the image forming apparatus has seven color image forming portions of red toner, green toner, and blue toner instead of the light cyan toner and light magenta toner in the first or second embodiment. Is performed in a portion other than a blue (Pg) image forming portion added to yellow (Pa), magenta (Pb), cyan (Pc), black (Pd), red (Pe), and green (Pf). Since this is exactly the same as the first or second embodiment, the description thereof will be omitted.

  The present invention can be applied to an electrophotographic image forming apparatus used in a copying machine, a printer, a facsimile, a plate making system, and the like.

FIG. 6 is a diagram for explaining a charge amount of toner in Embodiment 1 of the present invention. FIG. 6 is a diagram for explaining a change in charge amount of a first toner in Embodiment 1 of the present invention. FIG. 6 is a diagram for explaining a change in charge amount of a second toner in Embodiment 1 of the present invention. FIG. 6 is a diagram for explaining a change in charge amount of a third toner according to Embodiment 1 of the present invention. FIG. 6 is a diagram illustrating a change in charge amount of a fourth toner according to the first embodiment of the present invention. FIG. 6 is a diagram for explaining a change in charge amount of a fifth toner in the first embodiment. 6 is a diagram illustrating a change in the charge amount of a sixth toner according to Embodiment 1. FIG. 1 is a schematic view of a six-color image forming apparatus according to the present invention. 1 is a schematic view of a four-color image forming apparatus according to the present invention. FIG. 6 is a diagram for explaining a change in charge amount of toner by conventional four-color image formation. FIG. 6 is a diagram for explaining a change in charge amount of toner by conventional six-color image formation. It is sectional drawing of the image forming apparatus which concerns on Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Primary charger 4 Developing device 51 Intermediate transfer belt 64 Post-separation guide 78 Fixing part 58 Transfer part 57 Transfer roller (secondary transfer roller)
56 Opposite roller

Claims (3)

A photoconductive image carrier, a charging means for uniformly charging the image carrier, an exposure means for forming an electrostatic latent image by exposing the surface of the charged image carrier, and an electrostatic latent image Development means for forming a toner image by attaching toner, first transfer means for transferring the toner image on the image carrier to the intermediate image carrier, and the toner image on the intermediate image carrier as a recording material A second transfer means capable of contacting the intermediate image carrier for transferring, and transporting the recording material onto which the toner image on the intermediate image carrier has been transferred to a fixing member to obtain the toner image on the recording material; In the image forming apparatus having the fixing member that sandwiches and fixes the recording material,
2. The image forming apparatus according to claim 1, wherein the developing unit includes five or more developing devices, and the charge amount of the toner is sequentially increased in the order of the transfer process by the first transfer unit.   2. The developing unit uses at least one of yellow, magenta, cyan and black and at least one of light yellow, light magenta, light cyan, light black, red, green, blue, white and transparent. The image forming apparatus described.   The toner image formed on the intermediate image carrier has all the toner images transferred onto the intermediate image carrier by the first transfer unit, and then collectively recorded by the second transfer unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is transferred to a material.

Images