JP2004029056A - Image forming device - Google Patents

Abstract

An object of the present invention is to form a good full-color image with high productivity, and to form a black image with high productivity, running cost and downtime.
A color toner image sequentially formed on a photosensitive drum for color image formation by yellow, magenta, and cyan developing units (4Y, 4M, 4C) is sequentially transferred onto an intermediate transfer belt (5a). The toner image is transferred to the recording material P at the first transfer portion N1. Further, the black toner image formed by the black developing device 12 on the photosensitive drum 9 for forming a black image is transferred to the recording material P in the second transfer portion N2. The color toner image is formed by a two-component developer having a magnetic carrier and a non-magnetic color toner, and the black toner image is formed by a one-component developer having a magnetic black toner.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that has two image carriers and forms toner images of two or more colors.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a method of forming a multicolor image and a full-color image in an electrophotographic image forming apparatus, there are generally two general methods. In the following description,
First, as shown in FIG. 5, a charging device 2, an exposure device 3, developing devices 4C, 4Y, 4M, 4B, a transfer device 5, a transfer drum 21 are arranged around one photosensitive drum 1 rotating in the direction of arrow R1. And other process equipment. The toner images of each color (cyan, yellow, magenta, and black) sequentially formed on the photosensitive drum 1 are sequentially transferred and superimposed on the recording material P carried on the transfer drum 21 rotating in the direction of arrow R5. The recording material P after the transfer of the toner image is fixed on the surface by a fixing device (fixing unit) 20. This method is, for example, a method described as an example in JP-A-4-156474, and is hereinafter referred to as a "one-drum method". Reference numeral 7a in the figure denotes a cleaning device for removing unnecessary toner on the photosensitive drum 1.
[0003]
Second, as shown in FIG. 6, the four image forming units SB, SY, SM, and SC for black, yellow, magenta, and cyan are moved along the moving direction of the transfer belt 22 (the direction of arrow R22). They are arranged side by side. Each image forming unit has a photosensitive drum 1 and process devices such as a charging device 2, an exposure device 3, a developing device 4, a transfer device 5, and a cleaning device 7 arranged around the photosensitive drum 1. The black, yellow, magenta, and cyan toner images formed on the image forming stations SB, SY, SM, and SC are sequentially transferred and superimposed on the recording material P carried on the surface of the transfer belt 22. The recording material P after the transfer of the toner image is separated from the transfer belt 22 and conveyed to the fixing device 20, where it is heated and pressed to form a toner image on the surface. This method is a method described as another embodiment in, for example, JP-A-4-156474, and is hereinafter referred to as a "four-drum method".
[0004]
In the above-described "one-drum type" image forming apparatus, the color developing units 4M, 4Y, 4C, and 4B of the developing device (developing unit) 4 sequentially form the photosensitive drum 1, as shown in FIG. Rather than sequentially transferring the toner images of each color onto the recording material P, the toner images are temporarily primary-transferred onto the intermediate transfer belt 5a by an electric field of a transfer roller (transfer member) 5b, and then transferred onto the intermediate transfer belt 5a. A method of fixing the unfixed toner image after collectively transferring the four color toner images onto the recording material P by the electric field of the secondary transfer roller 6 is also described in, for example, JP-A-3-192282. Have been. Reference numeral 4a in the figure denotes a rotating body that rotates with each developing device mounted thereon, 5c denotes a driving roller, 6 denotes a secondary transfer roller, 7a denotes a cleaning device for cleaning the surface of the photosensitive drum 1, and 7b denotes an intermediate device. This is an intermediate transfer member cleaning device for cleaning the transfer belt 5a.
[0005]
Similarly, in the “four-drum type” image forming apparatus, the toner images of the respective colors formed by the image forming units SM, SC, SY, and SB are not transferred to the recording material P but to the intermediate transfer, as shown in FIG. Primary transfer is performed once by the electric field of the transfer blade (transfer member) 5b at each transfer portion on the belt 5a, and thereafter, the four color toner images on the intermediate transfer belt 5a are collectively recorded by the electric field of the secondary transfer roller 6. A method of fixing an unfixed toner image after transfer onto the material P is also described in, for example, JP-A-3-191368. Note that reference numeral A in the figure indicates the moving direction of the intermediate transfer belt 5a. 5d is a driven roller.
[0006]
The method using the intermediate transfer belt 5a shown in FIG. 7 and FIG. 8 is performed when the transfer drum 21 of the “1-drum type” in FIG. 5 is used and on the transport belt 22 of the “4-drum type” in FIG. Compared to the method of holding, transporting, and sequentially transferring the recording material P, the degree of freedom of arrangement of each device in the image forming apparatus is increased, so that the image forming apparatus can be downsized and various kinds of recording materials can be handled. In recent years, it has been used favorably from the viewpoint of possibility, and has become the mainstream of color image forming apparatuses.
[0007]
In the case of the former “one-drum method” of the above two methods, four toner images are formed using one photosensitive drum 1. By matching the above, even if the rotation of the photosensitive drum 1 fluctuates, the effect of the rotation fluctuation of the photosensitive drum 1 appears in the toner image of each color in the same manner. By matching the image forming positions, there is a feature that a change in hue is unlikely to appear even when uneven development density occurs due to fluctuations in the rotation of the photosensitive drum 1. In addition, among the process devices around one photosensitive drum 1, the same device can be used for each color except for the developing device, so that the configuration of the device can be simplified, and the device can be reduced in size and cost. It also has the feature that cost reduction is possible.
[0008]
However, in the “one-drum method”, it takes about four times as long to form a full-color image using four colors of yellow, magenta, cyan, and black as compared to a case where an image of only one color is obtained with normal black. However, there is a problem that productivity of a full-color image per unit time is low.
[0009]
On the other hand, in the case of the latter "four-drum system", in order to form a full-color image using four colors of yellow, magenta, cyan, and black, the photosensitive drum 1 corresponding to each color in each of the image forming units SY, SM, SC, and SB. Since the formation of toner images of each color can be performed in parallel, the time required to obtain a full-color image is slightly increased as compared with the time required to obtain a single-color toner image of black only. And has the advantage that the productivity of full-color images per unit time is high.
[0010]
However, in the case of the "four-drum system", a plurality of photosensitive drums 1 corresponding to each color and a process device are required around the photosensitive drums 1. Therefore, the configuration of the apparatus is complicated, the size is increased, and the cost is increased. Has problems. Further, in the case of the “four-drum system”, since the photosensitive drums 1 for forming the toner images of the respective colors are different, if the development density unevenness caused by the characteristics of the respective photosensitive drums 1 occurs, the change of the hue and There is also a problem that the characteristics of each photosensitive drum 1 need to be highly stable in order to prevent this. Further, since the transfer positions of the respective photosensitive drums 1 are separated from each other, image misalignment is likely to occur during transfer, and image information is transferred while the recording material P moves from the first transfer position to the last transfer position. This requires an image memory for storing the image data, so that there is a problem that the apparatus becomes expensive also from this point. Further, the size of the device is increased.
[0011]
Because of the advantages and disadvantages described above, the “one-drum method” image forming method is used in full-color machines that are also used for black and white images. Currently, it is used in full-color dedicated machines that require a large amount of full-color images.
[0012]
Therefore, as a technique that can solve the problems of the “one-drum method” and the “four-drum method”, as shown in FIG. 9, a “two-drum method” is an intermediate method between the two. For example, it is described in JP-A-4-204871. This is provided with two image forming units S1 and S2 having photosensitive drums 1 and 9, respectively. Around the photosensitive drums 1, 9, charging devices 2, 10, exposure devices 3, 11, developing devices 4, 12, transfer devices 5, 13, cleaning devices 7, 14, and the like are arranged, respectively. Each of the developing devices 4 and 12 is provided with two developing units. Reference numeral 5e in the figure is a secondary transfer facing roller.
[0013]
As shown in FIG. 10, a "two-drum system" in which a photosensitive drum 1 for a color image forming unit and a photosensitive drum 9 for a black image forming unit are divided is also proposed in, for example, Japanese Patent Application Laid-Open No. Hei 7-244414. Have been. The "two-drum system" provides a full-color image at about 1/2 to 1/3 the productivity of a "one-drum system" when forming a black image. In addition, the productivity at the time of forming a black image is not inferior to that of an ordinary black-and-white copying machine or the like. It is possible to obtain a high-quality full-color image. Note that reference numeral 13 in the figure is a transfer device.
[0014]
In other words, the "two-drum system" is a system useful in the case where the ratio of black image formation is high and the full-color image formation is performed appropriately, compared with the "one-drum system" or the "four-drum system". It can be said that. Further, as shown in FIG. 10, the black image forming unit and the color image forming unit form the “two-drum system”, so that the photosensitive drums 1 and 9 of the black image forming unit and the color image forming unit are individually formed. Can replace and perform maintenance. Also, there is an advantage that even if one of the image forming units becomes incapable of forming an image, image formation can be continued in the remaining image forming units.
[0015]
Further, since the positional deviation of the image due to the use of the two photosensitive drums is small as compared with the “four-drum method”, it is not necessary to increase the position accuracy as in the four-drum method, and the two photosensitive drums 1 and 9 are used. This can minimize the cost increase. In addition, there is an advantage that the size of the image forming apparatus can be reduced at the same time.
[0016]
Incidentally, in the above-described "one-drum system", "two-drum system", and "four-drum system", the developing system of the developer is a two-component developing system using a two-component developer including a magnetic carrier and a non-magnetic toner. Is widely preferred and used. This is because, in the case of color toners in particular, it is difficult to colorize the magnetic toner because of the color of the magnetic substance itself. This is also because the density stability and the uniformity are superior to those of the non-magnetic one-component developing system.
[0017]
5 to 10, members having the same configuration and operation are denoted by the same reference numerals, and repeated description is omitted as appropriate.
[0018]
[Problems to be solved by the invention]
However, in the above-described two-component developing method using a two-component developer composed of a magnetic carrier and a non-magnetic toner, a phenomenon occurs in which the magnetic carrier deteriorates as the use progresses. This is because the non-magnetic toner is consumed every time an image is formed and is replenished as needed, but the magnetic carrier is not consumed every time an image is formed, and a role of applying a predetermined charge to the non-magnetic toner by frictional charging. Therefore, as the use proceeds, foreign matter such as toner adheres to the surface, and the charging ability is reduced. Under such circumstances, the non-magnetic toner cannot obtain a sufficient amount of charge, and as a result, image defects such as low density, uneven density, and fogged images may occur.
[0019]
For this reason, it is necessary to periodically replace the magnetic carrier, and the number of complicated operations increases. That is, for example, when the ratio of black image formation is high, it is necessary to frequently change the magnetic carrier for black, which increases the running cost and increases the downtime, which imposes a load on the user and the service person. It becomes.
[0020]
On the other hand, in a one-component developing method using a one-component developer made of a magnetic toner, the toner is consumed every time an image is formed, and is appropriately replenished as needed. In general, a magnetic blade system as shown in FIG. 3 is used as a means for applying electric charge to the toner. In the magnetic blade system, the magnetic toner is magnetically constrained on a developing sleeve 42B, which is a toner carrier containing a developing magnet 41B having a multi-pole configuration, and a magnetic blade 43B made of a ferromagnetic material such as iron is used as a developing magnet. The toner is frictionally charged by the magnetic field between the magnetic blades 41B and is regulated to a desired layer thickness on the magnetic blade 43B.
[0021]
In this method, since there is almost no cause for directly abrading the developing sleeve 42B, it is possible to extend the service life, and it is a useful method for realizing reduction of running cost and downtimeless, and is used favorably. I have.
[0022]
By the way, in the above-described non-magnetic toner and magnetic toner, there is a difference in the amount of electric charge applied to each toner due to the structure, for example, whether or not a magnetic material is included, or a limitation of a pigment. Generally, the amount of charge applied to the non-magnetic toner tends to increase. In the toner manufacturing method, if it is attempted to equalize the amount of charge applied, other problems such as color developability and fixability occur, so that it is practically impossible.
[0023]
Further, there is a correlation between the charge amount of the toner and the transfer electric field for obtaining a good image. Specifically, as the amount of charge applied to the toner increases, the transfer electric field for obtaining a good image needs to be increased. Further, even if the transfer electric field is too large, the toner is charged to the opposite polarity, so that the upper limit of the transfer electric field for obtaining a good image is determined. That is, the range of the appropriate transfer electric field is limited according to the charge amount of the toner.
[0024]
That is, in any of the above-described “one-drum system”, “two-drum system”, and “four-drum system”, when a two-component developer is used as the black developer, the running is performed when the black image formation ratio is high. This will increase costs and downtime.
[0025]
On the other hand, when a one-component developing method using a magnetic toner as a black developer is used, running costs and downtime can be reduced even when the black image formation ratio is high.
[0026]
However, in a system using an intermediate transfer member (intermediate transfer belt), it is necessary to execute batch transfer from the intermediate transfer member to a recording material. At that time, the charge amounts of the color toner and the black toner are different. For example, since the charge amount of the black toner is low, if the transfer electric field is set so as to transfer the black toner satisfactorily to the recording material, an image which is insufficiently transferred to the color toner, for example, the density of a color image is reduced. On the other hand, if the transfer electric field is set so as to transfer the color toner to the recording material satisfactorily, an image in which an excessive transfer electric field acts on the black toner, for example, a black toner image will be scattered. Further, even if the transfer electric field is set in the middle of the appropriate transfer electric field between the two, it is difficult to obtain a good image as a full-color image, because each defect is slightly reduced.
[0027]
Furthermore, since the intermediate transfer member is also used for the black toner image, two transfer steps (primary transfer and secondary transfer) are required, so that the ratio at which the toner image formed on the photosensitive drum is transferred to the recording material, The transfer efficiency is lower than that of the direct transfer system in which the image is directly transferred from the photosensitive drum to the recording material. As a result, it is necessary to use an excessive amount of toner to obtain a desired density. The replenishment interval was shortened, leading to an increase in running costs.
[0028]
Therefore, the present invention has a simple configuration and is easy to miniaturize, and can form a good full-color image with high productivity for full-color image formation, and high productivity and running for black image formation. It is an object of the present invention to provide an image forming apparatus capable of reducing cost and downtime.
[0029]
[Means for Solving the Problems]
The invention according to claim 1 is an image forming apparatus, comprising: a first image carrier, a plurality of color developing units, and an intermediate transfer member, wherein the plurality of color developing units are provided on the first image carrier. A color image forming unit configured to transfer the formed color toner image to a recording material at a first transfer unit via the intermediate transfer body; a second image carrier; and a black developing unit; A black image forming section for transferring the black toner image formed on the second image carrier to the recording material in the second transfer section, and fixing the color toner image and the black toner image transferred on the recording material. And a developing method of the color developing means and a developing method of the black developing means.
[0030]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the color developing unit adopts a two-component developing method using a two-component developer having a magnetic carrier and a non-magnetic color toner. The black developing means adopts a one-component developing method using a one-component developer having a magnetic black toner.
[0031]
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the color developing unit employs a one-component developing method using a one-component developer having a non-magnetic color toner, and the black developing unit includes And a one-component developing method using a one-component developer having a magnetic black toner.
[0032]
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, transfer of a color toner image from the intermediate transfer body to a recording material in the first transfer portion is performed. The strength of the electrolysis is different from the strength of the electrolysis when the black toner image is transferred from the second image carrier to the recording material in the second transfer portion.
[0033]
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, a distance between the first transfer unit and the second transfer unit is a length in a transport direction. Is set to be equal to or less than the minimum length of the recording material in the conveyance direction.
[0034]
According to a sixth aspect of the present invention, in the image forming apparatus, the image forming apparatus includes a first image carrier and a color developing unit, and transfers the color toner image formed on the first image carrier by the color developing unit to a first image carrier. A color image forming unit for transferring to a recording material in a first transfer unit, a second image carrier, and black developing means; and a black toner formed on the second image carrier by the black developing means. A black image forming unit for transferring an image to a recording material in a second transfer unit; and a fixing unit for fixing the color toner image and the black toner image transferred on the recording material, and a developing method of the color developing unit. And the developing method of the black developing means is different.
[0035]
The invention according to claim 7 is the image forming apparatus according to claim 6, wherein the color developing means adopts a two-component developing method using a two-component developer having a magnetic carrier and a non-magnetic color toner, The black developing means adopts a one-component developing method using a one-component developer having a magnetic black toner.
[0036]
The invention according to claim 8 is the image forming apparatus according to claim 6, wherein the color developing unit adopts a one-component developing method using a one-component developer having a non-magnetic color toner, and the black developing unit is And a one-component developing method using a one-component developer having a magnetic black toner.
[0037]
According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the sixth to eighth aspects, a color toner image is transferred from the first image carrier to a recording material in the first transfer unit. Wherein the strength of the transfer electrolysis at the time of transfer is different from the strength of the transfer electrolysis when the black toner image is transferred from the second image carrier to the recording material in the second transfer portion.
[0038]
According to a tenth aspect, in the image forming apparatus according to any one of the sixth to ninth aspects, a distance between the first transfer unit and the second transfer unit is a length in a transport direction. Is set to be equal to or less than the minimum length of the recording material in the conveyance direction.
[0039]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the components denoted by the same reference numerals have the same configuration or operation, and a repeated description thereof will be omitted as appropriate.
[0040]
<Embodiment 1>
FIG. 1 shows, as Embodiment 1, an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG. 1 is an electrophotographic (four color) full-color image forming apparatus, and FIG. 1 is a longitudinal sectional view schematically showing a schematic configuration thereof. Note that the image forming apparatus includes a printer, a copying machine, a facsimile, and the like.
[0041]
The image forming apparatus shown in FIG. 1 includes a color image forming unit that forms a color image (an image of a color other than black) and a black image forming unit that forms a black image. (Hereinafter referred to as “photosensitive drum”) 1 and 9. The photosensitive drum 1 (first image carrier) 1 is for forming a color image, and the photosensitive drum (second image carrier) 9 is for forming a black image. In the following, "color" means a color other than black (black), and "black" includes "full color". According to this, “color toner” means toner of a color other than black.
[0042]
A charging roller (charging device) 2, an exposing device 3, a developing device (color developing means) 4, an intermediate transfer belt are provided around the photosensitive drum 1 for forming a color image substantially in the rotation direction (direction of arrow R1). (Intermediate transfer member) 5a, transfer roller (transfer device) 5b, secondary transfer roller 6, cleaning device 7a, intermediate transfer member cleaning device 7b, and the like are provided.
[0043]
The charging roller 2 is in contact with the surface of the photosensitive drum 1 and is driven to rotate in the direction of the arrow R2 as the photosensitive drum 1 rotates in the direction of the arrow R1. A charging bias is applied to the charging roller 2 by a charging bias application power supply (not shown), and thereby the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity and potential.
[0044]
The exposure device 3 sequentially irradiates the charged surface of the photosensitive drum 1 with laser light from a laser writing unit in accordance with image information of each color of yellow (Y), magenta (M), and cyan (C) by laser light. The charge is removed to form an electrostatic latent image.
[0045]
The developing device 4 comprises a rotary unit 4a rotating in the direction of arrow R4 and three color developing units 4Y, 4M and 4C mounted on the rotary 4a. The yellow developing unit 4Y contains a non-magnetic yellow toner and a magnetic carrier. The magenta developing unit 4M contains a non-magnetic magenta toner and a magnetic carrier. Further, the cyan developing device 4C contains a non-magnetic cyan toner and a magnetic carrier. The developing device 4 is arranged such that a developing device of a color to be used for developing the electrostatic latent image on the photosensitive drum 1 is arranged at a developing position facing the surface of the photosensitive drum 1 by rotation of the rotary 4a in the direction of arrow R4. Has become. A developing bias is applied to the developing units 4Y, 4M, and 4C by a developing bias applying power source (not shown) to the electrostatic latent images for yellow, magenta, and cyan colors sequentially formed on the photosensitive drum 1 described above. As a result, the toner of each color is sequentially attached and developed as a color toner image of each color.
[0046]
The intermediate transfer belt 5a is wound around a plurality of rollers and is driven to rotate in the direction of arrow R5. A primary transfer roller 5b is disposed inside the intermediate transfer belt 5a, and presses the intermediate transfer belt 5a against the surface of the photosensitive drum 1. A primary transfer bias is applied to the primary transfer roller 5b from a primary transfer bias application power source (not shown), whereby the color toner images of each color on the photosensitive drum 1 are sequentially transferred onto the intermediate transfer belt 5a and superimposed. Is done.
[0047]
The secondary transfer roller 6 transfers the color toner image on the intermediate transfer belt 5a to a recording material P such as paper, and rotates in the direction of arrow R6. The recording material P is stored in a paper feed cassette 30 and supplied at a predetermined timing by a feeding / conveying means (not shown) to a first transfer portion (transfer nip portion) between the intermediate transfer belt 5a and the secondary transfer roller 6. N1. At this time, a secondary transfer bias is applied to the secondary transfer roller 6 from a secondary transfer bias application power source (not shown), whereby the three color toner images on the intermediate transfer belt 5a are formed on the recording material P. The secondary transfer is performed at once.
[0048]
The cleaning device 7a removes color toner (residual toner) remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 5a when the color toner image on the photosensitive drum 1 is transferred to the intermediate transfer belt 5a. It is.
[0049]
When the color toner image on the intermediate transfer belt 5a is transferred to the recording material P, the intermediate transfer body cleaning device 7b removes the color toner (residual toner) remaining on the intermediate transfer belt 5a without being transferred to the recording material P. It is to be removed.
[0050]
On the other hand, a charging roller (charging device) 10, an exposing device 11, a developing device (black developing means) 12, and a transfer device around the photosensitive drum 9 for forming a black image are arranged in this order along the rotation direction (the direction of arrow R9). A roller (transfer device) 13, a cleaning device 14, and the like are provided.
[0051]
The charging roller 10 rotates in the direction of arrow R10, and uniformly charges the surface of the photosensitive drum 9 to a predetermined polarity and potential. The exposure device 11 irradiates the charged photosensitive drum 9 surface with laser light in accordance with image information to form an electrostatic latent image for black. The developing device 12 develops a black toner image by attaching black toner to the electrostatic latent image. The transfer roller 13 is in contact with the surface of the photosensitive drum 9 to form a second transfer portion (transfer nip portion) N2 between the transfer roller 13 and the photosensitive drum 9, and rotates in the direction of arrow R13. The recording material P on which the yellow, magenta, and cyan color toner images have been transferred to the surface in the above-described first transfer portion N1 is transferred to the black on the photosensitive drum 9 by the transfer roller 13 in the second transfer portion N2. The toner image is transferred.
[0052]
The recording material P onto which the four full-color toner images have been transferred in this manner is conveyed to the fixing device 20, where it is heated and pressed to fix the four full-color toner images on the surface. Thus, four full-color images are formed on the recording material P. On the other hand, the black toner (residual toner) remaining on the photosensitive drum 9 without being transferred to the recording material P is removed by the cleaning device 14.
[0053]
Hereinafter, each device and each member described above will be described in detail.
[0054]
[Photosensitive drum]
In the present embodiment, an OPC (organic optical semiconductor) photosensitive member having a diameter of 80 mm as the photosensitive drum 1 for forming a color image and a diameter of 30 mm as the photosensitive drum 9 for forming a black image is used. Each is a negatively charged photoconductor (negative photoconductor) composed of a conductive drum base made of aluminum or the like and a photoconductive layer (photoconductive layer) formed on the outer peripheral surface thereof. It is driven to rotate at a process speed (peripheral speed) of 150 mm / sec in the directions of the arrows R1 and R9.
[0055]
[Charging roller (charging device)]
Each of the charging rollers 2 and 10 is a roller having a composite layer structure including a center metal core, an elastic conductive layer formed concentrically and integrally with the outer periphery of the roller, and a resistance layer formed on the outer peripheral surface thereof. .
[0056]
The elastic conductive layer is, for example, 10 ⁴ It is formed of a single layer or a composite layer of a conductive rubber of Ω · cm or less. The resistance layer is 10 ⁷ -10 ¹¹ It is a single layer or a composite layer of a conductive rubber or the like having a thickness of about Ω · cm and about 100 μm or less.
[0057]
The charging rollers 2 and 10 are rotatably supported at both ends of the metal core by bearing members (not shown), and are pressed against the surfaces of the photosensitive drums 1 and 9 with a predetermined pressing force by pressing means (not shown). Have been. In the present embodiment, the photosensitive drums 1 and 9 are driven to rotate in the directions of the arrows R2 and R10, respectively, as the photosensitive drums 1 and 9 are driven to rotate in the directions of the arrows R1 and R9. When a predetermined charging bias is applied to the metal cores of the charging rollers 2 and 10 by a charging bias application power supply (not shown), the outer peripheral surfaces (surfaces) of the photosensitive drums 1 and 9 have a predetermined polarity (contact surface charging method). In the present embodiment, the charging process is performed uniformly to a minus potential.
[0058]
[Exposure equipment]
The exposure device 3 sequentially irradiates the charged photosensitive drum 1 surface with laser light based on image information of each color of yellow, magenta, and cyan. Further, the exposure device 11 irradiates the charged photosensitive drum 9 surface with laser light based on the black image information. These pieces of image information are obtained by reading an image of a document as image information of four colors of yellow, magenta, cyan, and black by an image reading device (not shown), or transferring image information of four colors from a personal computer or the like. The image information of the four colors is subjected to predetermined image processing by an image processing unit. The image information of the four colors of yellow, magenta, cyan and black is sent to a laser writing unit (not shown) in synchronization with, for example, the reading operation of the image reading device.
[0059]
[Color developing device]
The three color developing units 4M, 4Y, and 4C mounted on the rotary 4a of the developing device 4 all have the same configuration, and all employ a two-component developing system. Each developing device contains a developer in which a non-magnetic color toner and a magnetic carrier are mixed at a predetermined ratio, and the developer is restrained on a developing sleeve containing a magnet so as to perform development. It has become.
[0060]
FIG. 2 is an enlarged vertical sectional view of the magenta developing device 4M. The magenta developing device 4M has a developing container 46M for storing a two-component developer. The magenta two-component developer is a mixture of a non-magnetic magenta toner (open circles in the figure) and a magnetic carrier (black circles in the figure) at a predetermined ratio. Agents etc. are mixed. The developing device 4M includes a six-pole (N1, S1, N2, S2, N3, S3) cylindrical magnet 41M having a magnetic force of about 500 to 1000 Gauss, and a non-magnetic developing sleeve 42M having a diameter of 24 mm and including the magnet 41M. , A magnetic blade 43M facing the N1 pole position, and stirring members 44M and 45M. When the nonmagnetic magenta toner is stirred by the stirring members 44M and 45M, the nonmagnetic magenta toner is rubbed (sliding) with the magnetic carrier and charged to a predetermined charge amount. In the present embodiment, a charge amount of −18 μC / mg is given to the magenta toner.
[0061]
The magenta toner and the magnetic carrier to which the charge is applied are magnetically regulated between the N1 pole of the magnet 41M and the magnetic blade 43M by the rotation of the developing sleeve 42M in the direction of the arrow R4. Coated uniformly on 42M. As a developing method, a non-contact, non-magnetic developing sleeve 42M is disposed on the color image forming photosensitive drum 1 (see FIG. 1), and at this time, the coating layer of the toner and the magnetic carrier is used for the color image forming photosensitive drum. 1. In the state where the coating layer of the developer is in contact with the photosensitive drum 1, a developing bias in which a DC voltage is superimposed on a predetermined alternating voltage is applied to the developing sleeve 42M.
[0062]
In the present embodiment, color image formation is performed by applying a developing bias in which a DC voltage of -350 V is superimposed on an alternating voltage composed of a rectangular wave having a peak-to-peak voltage Vpp of 1.5 kV and a frequency of 2.0 kHz to the non-magnetic sleeve 42M. A two-component developing method in which magenta toner is adhered to the electrostatic latent image on the photosensitive drum 1 for development to perform development.
[0063]
The cyan developing unit 4C and the yellow developing unit 4Y have the same configuration as the above-described magenta developing unit 4M, and differ only in the color of the color toner.
[0064]
Further, all the color toners in the present embodiment have negative polarity (negative toner).
[0065]
[Black (black) developing unit]
As shown in FIG. 3, the black developing device 12 includes a developing container 46B for storing a magnetic one-component toner (black circles in FIG. 3) and four poles (S1, N1, S2, An N2) magnet 41B, a non-magnetic developing sleeve 42B having a diameter of 20 mm and enclosing the magnet 41B, and a magnetic blade 43B facing the N1 pole position are provided. The magnetic toner is charged to a predetermined charge by receiving a magnetic binding force and friction between the N1 pole of the magnet 41B and the magnetic blade 43B. In the present embodiment, a charge amount of −11 μC / mg is given to the black toner.
[0066]
The thickness of the black toner to which the charge is applied is magnetically regulated between the N1 pole of the magnet 41B and the magnetic blade 43B by the rotation of the developing sleeve 42B in the direction of arrow R12, and the black toner is placed on the non-magnetic developing sleeve 42B. Uniformly coated. In the developing method, a non-magnetic developing sleeve 42B is provided in non-contact with the photosensitive drum 9 for forming a black image, and the toner coating layer is also disposed so as not to contact the photosensitive drum 9 for forming a black image. . In this state, a developing bias in which a DC voltage is superimposed on a predetermined alternating voltage is applied to the developing sleeve 42B.
[0067]
In this embodiment, black image formation is performed by applying a developer bias in which a DC voltage of -500 V is superimposed on an alternating voltage formed of a rectangular wave having a peak-to-peak voltage Vpp of 1.0 kV and a frequency of 1.8 kHz to the developing sleeve 42B. A one-component developing system for developing an electrostatic latent image on a photosensitive drum 9 was used.
[0068]
In the present embodiment, the black toner is a negative toner.
[0069]
[Intermediate transfer belt (intermediate transfer body)]
As shown in FIG. 1, the intermediate transfer belt 5a is an endless belt that is held flat over a region including the transfer portion of the photosensitive drum 1 for forming a color image. On the intermediate transfer belt 5a, color toner images of each color sequentially formed on the photosensitive drum 1 for forming a color image are sequentially primary-transferred and superimposed. The circumference of the intermediate transfer belt 5a is an integral multiple (for example, 2 to 5 times) of the circumference of the photosensitive drum 1 for forming a color image. In the present embodiment, the circumference is set to 2 × 80 × π (mm). The intermediate transfer belt 5a is formed of a single layer of conductive rubber, has a thickness of 100 μm, and has a resistance of 1 × 10 ⁹ Ω. The intermediate transfer belt 5a is driven by three rollers including a drive roller driven by a drive mechanism (not shown) at the same speed as the process speed (peripheral speed) in synchronization with the rotation of the photosensitive drum 1. It can be circulated along the direction of arrow R5.
[0070]
A transfer roller (primary transfer roller) 5b is provided inside the intermediate transfer belt 5a so as to press the intermediate transfer belt 5a against the photosensitive drum 1. The transfer roller 5b is for transferring the toner image of each color formed on the photosensitive drum 1 for forming a color image onto the intermediate transfer belt 5a. The transfer roller 5b includes a central metal core and a medium-resistance elastic layer formed concentrically and integrally with the outer periphery of the core metal. The transfer roller 5b in the present embodiment has a resistance of 5 × 10 ⁶ Ω, a conductive rubber roller having a diameter of 16 mm.
[0071]
By applying a predetermined transfer bias (positive in the present embodiment) having a polarity opposite to that of the color toner image from a transfer bias application power supply (not shown) to the core metal portion of the transfer roller 5b, The color toner images are sequentially and primarily transferred onto the intermediate transfer belt 5a, and these color toner images are superimposed on the intermediate transfer belt 5a.
[0072]
[Transfer roller]
The transfer roller (secondary transfer roller) 6 transfers a color toner image primarily transferred and carried on the intermediate transfer belt 5a to a recording material P such as paper. The transfer roller 6 includes a central core metal and a medium-resistance elastic layer formed concentrically and integrally with the outer periphery of the core metal. The transfer roller 6 in the present embodiment has a resistance of 5 × 10 ⁸ Ω, a conductive rubber roller having a diameter of 16 mm.
[0073]
By applying a predetermined transfer bias (positive in the present embodiment) having a polarity opposite to that of the color toner image to the core portion of the transfer roller 6 by a secondary transfer bias application power source (not shown), the intermediate transfer belt 5a is applied. The three color toner images are collectively and secondarily transferred to the recording material P.
[0074]
On the other hand, the transfer roller 13 transfers the black toner image formed on the photosensitive drum 9 for forming a black image onto the recording material P. The transfer roller 13, like the transfer roller 6, includes a central metal core and a medium-resistance elastic layer formed concentrically and integrally with the outer periphery of the metal core. The transfer roller 13 in the present embodiment has a resistance of 5 × 10 ⁸ Ω, a conductive rubber roller having a diameter of 16 mm.
[0075]
In the transfer roller 13, similarly to the transfer roller 6, a predetermined bias (positive in the present embodiment) having a polarity opposite to that of the black toner image is applied to the metal core by a transfer bias application power supply (not shown). Then, the black toner image on the photosensitive drum 9 for forming a black image is transferred to the recording material P.
[0076]
Here, a first transfer portion N1 formed between the transfer roller 6 and the intermediate transfer belt 5a, and a second transfer portion (second transfer nip) formed between the transfer roller 13 and the photosensitive drum 9 The distance L from the recording medium P is set shorter than the length of the recording material P having the minimum length in the conveyance direction. In the present embodiment, L is set to 80 mm because the distance of the short side of the postcard made by government, that is, 100 mm is the minimum value of the length of the recording material P in the transport direction.
[0077]
In the image forming apparatus having the above-described configuration, four full-color images are formed as follows.
[0078]
Here, first, a case of forming a full-color image of four colors of yellow, magenta, cyan, and black using the image forming apparatus will be described, and then, a case of forming only a black image will be described.
[0079]
In the above-described image forming apparatus, as shown in FIG. 1, after the surface of a photosensitive drum 1 for forming a color image is uniformly charged by a charging roller 2, the exposure device 3 is irradiated with a yellow image signal. Exposure for yellow is performed by the laser light from, and an electrostatic latent image for yellow is formed on the photosensitive drum 1. The yellow electrostatic latent image formed on the photosensitive drum 1 is developed by the yellow developing device 4Y of the developing device 4 to become a yellow toner image. The yellow toner image formed on the photosensitive drum 1 is transferred onto the intermediate transfer belt 5a by the transfer roller 5b. After the transfer of the yellow toner image, the surface of the photosensitive drum 1 is cleaned by the cleaning device 7a.
[0080]
Thereafter, a magenta toner image and a cyan toner image are sequentially formed on the photosensitive drum 1 by the same image forming process as described above, and these toner images are sequentially superimposed and transferred onto the intermediate transfer belt 5a.
[0081]
Next, in order to transfer the color toner image formed on the intermediate transfer belt 5a to a desired recording material P, the recording material P is fed from the sheet feeding cassette 30 by a pickup unit (not shown). The fed recording material P is conveyed to a first transfer unit N1 by a synchronization unit (not shown) at a predetermined timing, that is, at a desired position on the recording material P to transfer the toner image. The color toner images of the respective colors on the intermediate transfer belt 5a are collectively transferred to the recording material P conveyed to the first transfer portion N1 by the transfer bias applied to the transfer roller 6.
[0082]
At this time, a constant current of 20 μA is passed through the transfer roller 6 as a transfer current.
[0083]
By the way, with respect to this transfer current, the following results were obtained by the present inventors in the configuration of the present embodiment. When the transfer current is lower than 17 μA, the transferability is deteriorated and the concentration is reduced. On the other hand, when the current exceeds 23 μA, the toner is charged to the opposite polarity, and a phenomenon called retransfer, that is, a phenomenon in which partial image omission or scattering of line images is deteriorated occurs.
[0084]
The residual toner remaining on the surface of the intermediate transfer belt 5a after the transfer of the color toner image is removed by the intermediate transfer body cleaning device 7b. Note that the intermediate transfer body cleaning device 7b can come in contact with and separate from the intermediate transfer belt 5a at a predetermined timing. That is, after the three color toner images are transferred onto the recording material P, the three color toner images are brought into contact with the surface of the intermediate transfer belt 5a.
[0085]
After the transfer of the color toner image, the recording material P is conveyed toward the second transfer portion N2 on the downstream side.
[0086]
On the photosensitive drum 9 for forming a black image, a black toner image is formed. At this time, when the electrostatic latent image for cyan, which is the final color of the above-described color toner image, is written by the laser beam, the black toner image matches the color toner image already transferred on the recording material P. An electrostatic latent image for black is formed on the photosensitive drum 9 by a laser beam irradiated according to an image signal for black with a delay so that the image is transferred. In other words, instead of starting the image exposure for black after the formation of the cyan toner image, which is the final color of the above-described color toner image, is completed, the image is synchronized with the color toner image on the recording material P. The image formation for black is started.
[0087]
Therefore, the image processing unit that processes the image information read by the above-described image reading apparatus includes an image memory that temporarily stores all or a part of the black image information.
[0088]
After the photosensitive drum 9 is uniformly charged by the charging roller 10, as described above, the photosensitive drum 9 is exposed to the black light by the laser beam emitted from the exposure device 11 in accordance with the black image signal, and On the drum 9, an electrostatic latent image for black is formed. This electrostatic latent image is developed by the black developing device 12 to become a black toner image. The black toner image thus formed on the photosensitive drum 9 is aligned with the color toner image on the recording material P in the second transfer portion N2 by applying a transfer bias to the transfer roller 13. Transcribed so as to overlap.
[0089]
At this time, a constant current of 12 μA is passed through the transfer roller 6 as a transfer current.
[0090]
By the way, with respect to this transfer current, the following results were obtained by the present inventors in the configuration of the present embodiment. When the transfer current is lower than 9 μA, the transferability is deteriorated and the density is reduced. On the other hand, if it exceeds 15 μA, the toner is charged to the opposite polarity, and a phenomenon called retransfer, that is, a phenomenon in which partial image omission or scatter of line drawing worsens occurs.
[0091]
After the transfer of the black toner image, the surface of the photosensitive drum 9 is cleaned by removing the residual toner by the cleaning device 14.
[0092]
Thereafter, the four color toner images of yellow, magenta, cyan, and black transferred on the recording material P are fixed on the recording material P by the transfer device 20. Thus, four full-color images are formed, and the image forming process is completed.
[0093]
In this case, the other color toner images formed besides the black toner image are not limited to all three colors of yellow, magenta, and cyan, and one of these colors may be appropriately selected or two colors may be mixed. Needless to say, the color may be obtained by the following method. The image forming process in this case is performed according to the above-described full-color image forming process.
[0094]
Subsequently, a case where only the black image is formed using the image forming apparatus having the above-described configuration will be described.
[0095]
That is, in the above-described image forming apparatus, after the surface of the photosensitive drum 9 for forming a black image is uniformly charged by the charging roller 10, the black image is formed by the laser beam emitted from the exposure device 11 in accordance with the black image signal. Is performed, and a black electrostatic latent image is formed on the photosensitive drum 9. This electrostatic latent image is developed by the black developing device 12 to form a black toner image, as in the case described above.
[0096]
Next, in order to transfer the black toner image formed on the photosensitive drum 9 to a desired recording material P, the recording material P is fed from the paper feed cassette 30 by a pickup unit (not shown). The black toner image on the photosensitive drum 11 is transferred to the recording material P introduced into the second transfer portion N2 by a transfer bias applied to the transfer roller 13.
[0097]
At this time, the transfer bias applied to the transfer roller 13 is such that a constant current of 12 μA flows as the transfer current, as in the case of full-color image formation.
[0098]
After the transfer of the black toner image, the recording material P is conveyed to the fixing device 20, and the black toner image is fixed on the surface. As a result, a black image is formed, and the black-only image forming process ends.
[0099]
As described above, in the case of the image forming apparatus according to the present embodiment, it is possible to obtain a stable black image required for a black-and-white full-color machine and to use a large number (three or more) of photosensitive drums. Therefore, it is possible to obtain a high-quality full-color image free from color shift and color unevenness caused by the characteristics of the photosensitive drum.
[0100]
Also, regarding the image misregistration due to the use of the two photosensitive drums 1 and 9, only the black image for the color image is used, so two developing units are arranged for each of the two photosensitive drums 1 and 9. As compared with the conventional method (the image forming apparatus shown in FIG. 9), the positional accuracy is looser, so that the cost increase due to the use of the two photosensitive drums 1 and 9 can be minimized.
[0101]
Further, by setting the distance between the first transfer portion N1 and the second transfer portion N2 to be equal to or less than the minimum length of the recording material, a special conveyance path is not required. It is possible to improve the productivity of black image formation and to form a good color image without increasing the cost.
[0102]
Further, by adopting a method of directly transferring the black toner image from the photosensitive drum 9 for forming a black image to the recording material P, a desired image density (black image density) can be obtained with a smaller amount of developer. And the running cost can be reduced. Furthermore, since the color image forming section is not operated during the formation of the black image, the color image forming section requires only a minimum necessary operation, and as a result, the running cost can be similarly reduced.
[0103]
Further, it is possible to obtain a stable full-color image in which the productivity of a full-color image is about 1/3 of the productivity of a black image, while being inexpensive and compact.
[0104]
Further, the transfer positions of the color toner image and the black toner image on the recording material P are divided into a first transfer portion N1 and a second transfer portion N2 as shown in FIG. It is possible to apply an optimal transfer electric field (transfer bias) to the image, and to prevent image defects depending on the strength of the transfer electric field such as low density and toner scattering at both color image formation and black image formation. It is possible to always provide a good image.
[0105]
Furthermore, by using a magnetic one-component toner in the black image forming unit, even if the image forming ratio is biased toward black, for example, there is no need to replace the magnetic carrier, thereby reducing running costs and downtime. Can be realized.
[0106]
<Embodiment 2>
FIG. 4 shows a schematic configuration of an image forming apparatus according to the second embodiment.
[0107]
In the present embodiment, the color image forming section has a configuration of only one color. That is, in the image forming apparatus shown in FIG. 1 of the first embodiment, instead of forming the three color toner images of yellow, magenta, and cyan in the color image forming unit, In the color image forming section, a color toner image of only one color of magenta is formed. Accordingly, the intermediate transfer belt 5a and the transfer roller 5b, which are required in the first embodiment, are omitted.
[0108]
Next, the operation of the present embodiment when forming two color toner images of magenta and black will be described.
[0109]
As shown in FIG. 4, the image forming apparatus according to the present embodiment is configured such that after the surface of a photosensitive drum 1 for forming a color image is uniformly charged by a charging roller 2, an exposure device is provided in accordance with a magenta image signal. Exposure for magenta is performed by the laser light emitted from the 3M, whereby an electrostatic latent image for magenta is formed on the photosensitive drum 1. This electrostatic latent image is developed by a magenta developing unit 4M to become a magenta toner image. At this time, the recording material P is picked up by the pickup means (not shown) and the synchronizing means (not shown) from the paper feeding cassette 30 at a predetermined timing, that is, at a desired position on the recording material P to transfer the magenta toner image. 1 is transferred to the transfer section N1. The magenta toner on the photosensitive drum 1 is transferred to the recording material P introduced into the first transfer portion N1 by the transfer bias applied to the transfer roller 6.
[0110]
At this time, a constant current of 20 μA flows through the transfer roller 6 as a transfer current.
[0111]
As for the transfer current, as in the first embodiment, when the transfer current is lower than 17 μA, the transferability deteriorates and the density decreases. On the other hand, if it exceeds 23 μA, it is known that the toner is charged to the opposite polarity, and a phenomenon called retransfer, that is, a phenomenon in which partial image omission or scatter of line drawing worsens occurs.
[0112]
The recording material P on which the magenta toner image has been transferred at the first transfer portion N1 is transported toward the second transfer portion N2 on the downstream side.
[0113]
On the other hand, the surface of the photosensitive drum 1 after the transfer of the magenta toner image is cleaned by the cleaning device 7a to remove the residual toner.
[0114]
On the photosensitive drum 9 for forming a black image, a black toner image is formed. At this time, the writing of the electrostatic latent image for magenta by the laser light is delayed so that the black toner image is transferred in accordance with the magenta toner image transferred onto the recording material P. As a result, a black electrostatic latent image is formed on the photosensitive drum 9 by a laser beam irradiated according to a black image signal. In other words, instead of starting the image exposure for black after the formation of the magenta toner image is completely completed, the formation of the black toner image is started in synchronization with the magenta toner image on the recording material P. It has become.
[0115]
Therefore, the image processing unit that processes the image information read by the above-described image reading apparatus includes an image memory that temporarily stores all or a part of the black image information.
[0116]
After the photosensitive drum 9 is uniformly charged by the charging roller 10, as described above, the photosensitive drum 9 is exposed to the black light by the laser light emitted from the exposure device 11 in accordance with the black image signal. An electrostatic latent image for black is formed thereon. This electrostatic latent image is developed by the black developing device 12 to become a black toner image. The black toner image thus formed on the photosensitive drum 9 is overlapped with the magenta toner image on the recording material P in the second transfer portion N2 by the transfer bias applied to the transfer roller 13. Transcribed.
[0117]
At this time, a constant current of 12 μA flows through the transfer roller 6 as a transfer current.
[0118]
As in the first embodiment, when the transfer current is lower than 9 μA, the transferability deteriorates and the density decreases. On the other hand, if it exceeds 15 μA, the toner is charged to the opposite polarity, and a phenomenon called retransfer, that is, a phenomenon in which partial image omission or scattering of line images worsens occurs.
[0119]
The cleaning device 14 removes the residual toner remaining on the surface of the photosensitive drum 11 after the transfer of the black toner image.
[0120]
On the other hand, the recording material P after the transfer of the black toner image is fixed by the fixing device 20, whereby the image formation by magenta and black is completed.
[0121]
The image formation using only the black toner is the same as in the first embodiment, and a description thereof will not be repeated.
[0122]
In the configuration of the present embodiment, in the two-color (magenta and black) image forming apparatus, as in the first embodiment, it is possible to improve the productivity at the time of forming a black image, reduce running costs, and reduce downtime. While the magenta and black images are being formed, direct transfer from the photosensitive drum 1 for forming a color image to the recording material P is being performed. In the embodiment, a desired density can be obtained with magenta, and a reduction in running cost can be realized.
[0123]
In the present embodiment, a color image is formed using magenta toner. However, the present invention is not limited to this, and any color toner other than black can be used. Of course.
[0124]
<Embodiment 3>
In the first and second embodiments, the two-component developing method including the magnetic carrier and the non-magnetic color toner has been described as the color developing method. However, in the present embodiment, the color developing method is a two-component developing method. Instead of the component development system, a non-magnetic one-component development system known in the art was used.
[0125]
In other words, the color developer uses only non-magnetic color toner. According to this method, since a magnet (for example, 41M in FIG. 2) in the developing device is not required, color image formation can be performed with a cheaper configuration. In addition, instead of the magnetic blade, the elastic blade made of silicon rubber or the like is used to frictionally charge the non-magnetic color toner in contact with the developing sleeve and coat it electrostatically instead of the magnetic blade. Can be realized by arranging them.
[0126]
The image forming apparatuses according to the first to third embodiments can be similarly configured not only as a copier integrated with an image reading unit but also as a printer having no image reading unit.
[0127]
Further, each component is not limited to those described in the above embodiments. For example, in Embodiments 1 to 3, a laser beam is used as an image writing unit. However, other writing units such as a diode array may be used, and a charging unit such as a corona charger instead of a charging roller may be used as a charging unit. Means may be used, and other transfer means such as corona transfer may be used as the transfer means instead of the transfer roller.
[0128]
In addition, various bias settings, process speeds, and the like are not limited to the present embodiment, but include modes that do not depart from the technical idea.
[0129]
【The invention's effect】
As described above, according to the present invention, a black image can be formed at the time of forming a black image without reducing productivity. Further, since the black image forming section is a direct transfer from the first image bearing member to the recording material, it is possible to obtain a desired density with a smaller amount of developer and to reduce the running cost as compared with the method using an intermediate transfer member. Can be reduced. In addition, it is possible to form a high-quality full-color image without color unevenness due to color misregistration and characteristics of the image carrier.
[0130]
Furthermore, by separating the transfer portion of the color image forming portion and the black image forming portion onto the recording material, it is possible to select an optimum transfer electric field, and in a system in which a one-component developer and a two-component developer are mixed. Also, it is possible to always obtain a good image without excessive or insufficient transfer electric field.
[Brief description of the drawings]
FIG. 1 is a view schematically showing a longitudinal section of an image forming apparatus according to a first embodiment.
FIG. 2 is a longitudinal sectional view illustrating a configuration of a color developing device that performs development using a two-component developer.
FIG. 3 is a longitudinal sectional view illustrating a configuration of a black developing device that performs development with a one-component developer.
FIG. 4 is a diagram schematically illustrating a longitudinal section of an image forming apparatus according to a second embodiment.
FIG. 5 is a diagram illustrating a schematic configuration of a conventional image forming apparatus (one-drum type / transfer drum type).
FIG. 6 is a diagram illustrating a schematic configuration of a conventional image forming apparatus (four-drum type / transfer belt type).
FIG. 7 is a diagram illustrating a schematic configuration of a conventional image forming apparatus (one-drum type / intermediate transfer type).
FIG. 8 is a diagram showing a schematic configuration of a conventional image forming apparatus (four-drum type / intermediate transfer type).
FIG. 9 is a diagram illustrating a schematic configuration of a conventional image forming apparatus (two-drum type).
FIG. 10 is a diagram showing a schematic configuration of a conventional image forming apparatus (another two-drum system).
[Explanation of symbols]
1. First image carrier (photosensitive drum for color image formation)
4. Color developing means (color developing device)
4C cyan developer
4M magentan developer
4Y yellow developer
5a Intermediate transfer body (intermediate transfer belt)
9 Second image carrier (photosensitive drum for black image formation)
12 Black developing means (black developing device)
20 fixing means (fixing device)
L Distance between the first transfer unit and the second transfer unit
N1 First transfer portion (first transfer nip portion)
N2 Second transfer part (second transfer nip part)
P recording material

Claims (10)

A first image carrier, a plurality of color developing means, and an intermediate transfer body, wherein the color toner image formed on the first image carrier by the plurality of color developing means is passed through the intermediate transfer body; A color image forming section for transferring to a recording material in a first transfer section;
A black image forming apparatus including a second image carrier and a black developing unit, wherein a black toner image formed on the second image carrier by the black developing unit is transferred to a recording material in a second transfer unit; Department and
Fixing means for fixing the color toner image and the black toner image transferred on the recording material,
The developing system of the color developing unit is different from the developing system of the black developing unit.
An image forming apparatus comprising: The color developing means adopts a two-component developing method using a two-component developer having a magnetic carrier and a non-magnetic color toner, and the black developing means adopts a one-component developing method using a one-component developer having a magnetic black toner. Adopt the method,
The image forming apparatus according to claim 1, wherein: The color developing unit employs a one-component developing system using a one-component developer having a non-magnetic color toner, and the black developing unit employs a one-component developing system using a one-component developer having a magnetic black toner. ,
The image forming apparatus according to claim 1, wherein: The strength of transfer electrolysis when the color toner image is transferred from the intermediate transfer member to the recording material in the first transfer portion, and the black toner image from the second image carrier to the recording material in the second transfer portion The strength of the transfer electrolysis when transferring
The image forming apparatus according to claim 1, wherein: The distance between the first transfer unit and the second transfer unit is set to be equal to or less than the length of the recording material having the minimum length in the transport direction in the transport direction.
The image forming apparatus according to claim 1, wherein: A color image forming apparatus including a first image carrier and a color developing unit, wherein a color toner image formed on the first image carrier by the color developing unit is transferred to a recording material in a first transfer unit; Department and
A black image forming apparatus including a second image carrier and a black developing unit, wherein a black toner image formed on the second image carrier by the black developing unit is transferred to a recording material in a second transfer unit; Department and
Fixing means for fixing the color toner image and the black toner image transferred on the recording material,
The developing system of the color developing unit is different from the developing system of the black developing unit.
An image forming apparatus comprising: The color developing means adopts a two-component developing method using a two-component developer having a magnetic carrier and a non-magnetic color toner, and the black developing means adopts a one-component developing method using a one-component developer having a magnetic black toner. Adopt the method,
The image forming apparatus according to claim 6, wherein: The color developing unit employs a one-component developing system using a one-component developer having a non-magnetic color toner, and the black developing unit employs a one-component developing system using a one-component developer having a magnetic black toner. ,
The image forming apparatus according to claim 6, wherein: The strength of the transfer electrolysis when the color toner image is transferred from the first image carrier to the recording material in the first transfer unit, and the strength of the transfer electrolysis from the second image carrier to the recording material in the second transfer unit. The strength of the transfer electrolysis when transferring the black toner image is different,
The image forming apparatus according to any one of claims 6 to 8, wherein: The distance between the first transfer unit and the second transfer unit is set to be equal to or less than the length of the recording material having the minimum length in the transport direction in the transport direction.
The image forming apparatus according to any one of claims 6 to 9, wherein:

Images