JP2005010759A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which has respective functions of preventing the lowering of transfer rate, the re-transferring of toner and exfoliation discharge and in which a full color mode and a color reduction mode are made changable. <P>SOLUTION: The image forming apparatus has a transfer means which transfers a toner image onto an intermediate transfer body or a transfer material to form an image thereon, a selection means for selecting one mode among a plurality of modes including a first mode for forming the image by using a plurality of colors including a first color and a second mode for forming the image by using less number of colors including the first color than that of the colors in the first mode and a control means for controlling the transfer means in order that a transfer rate of a toner image of the first color in the second mode is larger than that of a toner image of the first color in the first mode when toner images are transferred onto the intermediate transfer body or the transfer material by the transfer means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that can be switched between a color mode and a subtractive color mode.

Conventionally, when transferring a toner image from a plurality of image carriers to an endless belt-like intermediate transfer member or a transfer material conveyed with the endless belt-like intermediate transfer member, it is possible to switch between a color mode and a color reduction mode. Conventional image forming apparatuses have the following two problems.
a) Separation discharge occurs when the toner image is separated from the image carrier after transfer due to a change in the resistance value of the endless belt-shaped intermediate transfer member or the transfer material, or due to an increase in the potential of the toner layer due to the superposition of a plurality of color toner images. .
b) When the toner transferred to the endless belt-shaped intermediate transfer member or the transfer material is transferred to the next color or the next color, the toner charge or polarity is changed and the toner is transferred again to the image carrier.

  In general, as measures for solving these problems, the toner adhesion amount is decreased, the toner charge amount is decreased, the resistivity of the endless belt-shaped intermediate transfer member is decreased, Attempts have been made to select a transfer output that is less likely to cause image generation. There have also been attempts to combine several countermeasures that do not cause the above-described phenomenon when toners of a plurality of colors, usually two or more colors, are overlapped.

  In addition, when only black toner is used when forming a monochrome image in a color image forming apparatus that uses four-color toner, the other three-color image carrier and an endless belt-shaped intermediate transfer member or a transfer material conveyed therewith There is also an image forming apparatus as shown in Patent Document 1 that is not brought into contact with the toner. In this case, only the transfer of black toner needs to be considered. Therefore, there is a disadvantage that the output is kept small and the monochrome mode image is insufficiently transferred.

  In the subtractive color mode using two-color toner, normally, the four image carriers and the endless belt-shaped intermediate transfer member are in contact with each other, and only two-color toner is used on the four image-bearing members. Transcription is not necessary. In this case, however, the toner on the endless belt-shaped intermediate transfer member is transferred to the remaining two-color image carrier when the two-color transferred image (toner image) passes through the transfer position of the remaining two-color image carrier. This causes a problem of re-transferring.

For example, as shown in Patent Document 2, each transfer unit is arranged with respect to four image carriers via an endless belt-shaped intermediate transfer member, and transfer of transfer units at two ends of the most upstream and the most downstream is performed. This is dealt with by making the output larger than the transfer output of the two transfer means in the center. In the multi-color mode, the transfer output of the transfer means at the two end portions is made larger than in the single-color mode, so retransfer is inevitable and a satisfactory result is not always obtained.
JP-A-11-249371 JP 2000-98758 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of solving the above-described problems in the prior art and forming a high-quality image. In particular, a first object is to provide an image forming apparatus capable of preventing a decrease in transfer rate and preventing toner retransfer. A second object is to provide an image forming apparatus capable of preventing peeling discharge in a transfer region.

In order to solve the above problems, according to a first aspect of the present invention, an image forming apparatus transfers a toner image to an intermediate transfer member or a transfer material, and forms an image on the intermediate transfer member or the transfer material. Transfer means for,
A plurality of modes including a first mode in which the image is formed using a plurality of colors including a first color and a second mode in which the image is formed using less colors than the first mode including the first color. Selecting means for selecting one mode from the modes;
The transfer rate of the toner image of the first color in the first mode when the toner image is transferred onto the intermediate transfer member or the transfer material by the transfer unit is greater than the transfer rate of the first color toner image in the second mode. And a control unit for controlling the transfer unit so that the transfer rate of the toner image of one color is increased.

  In the second mode, it is preferable to form the image using one color.

The image forming apparatus includes a plurality of image carriers on which the toner images of different colors are formed,
The transfer unit transfers the toner image formed on the image carrier onto the intermediate transfer member or the transfer material by bringing the intermediate transfer member or the transfer material into contact with the image carrier. ,
In the second mode, among the plurality of image carriers, the image carrier on which no toner image is formed is preferably separated from the intermediate transfer member or the transfer material.

  Preferably, the control unit controls a transfer rate of the toner image by controlling a current value or a voltage value of the transfer unit.

  When the intermediate transfer member is provided, the intermediate transfer member preferably has an endless belt shape.

  The image forming apparatus preferably includes an endless belt-shaped conveying unit that conveys the transfer material when the toner image is directly transferred to the transfer material without passing through the intermediate transfer member.

  The first mode is a full-color mode that uses the toner image formed on all of the plurality of image carriers, and the second mode is one image carrier among the plurality of image carriers. It is preferable that the monochrome mode uses the formed toner image.

According to a second aspect of the present invention, an image forming apparatus includes:
Transfer means for transferring a toner image to an intermediate transfer member or a transfer material, and forming an image on the intermediate transfer member or the transfer material;
One mode is selected from a plurality of modes including a first mode in which the image is formed using a first number of colors and a second mode in which the image is formed using a smaller number of colors than the first number. A selection means for selecting;
When at least one color used in the second mode when the toner image is transferred onto the intermediate transfer member or the transfer material by the transfer unit, the transfer rate of the toner image in the first mode is higher than the transfer rate of the toner image in the first mode. And a control unit for controlling the transfer unit so as to increase the transfer rate of the toner image in the second mode.

  In the second mode, it is preferable to form the image using one color.

The image forming apparatus includes a plurality of image carriers on which the toner images of different colors are formed,
The transfer unit transfers the toner image formed on the image carrier onto the intermediate transfer member or the transfer material by bringing the intermediate transfer member or the transfer material into contact with the image carrier. ,
In the second mode, among the plurality of image carriers, the image carrier on which no toner image is formed is preferably separated from the intermediate transfer member or the transfer material.

  Preferably, the control unit controls a transfer rate of the toner image by controlling a current value or a voltage value of the transfer unit.

  When the intermediate transfer member is provided, the intermediate transfer member preferably has an endless belt shape.

  The image forming apparatus preferably includes an endless belt-shaped conveying unit that conveys the transfer material when the toner image is directly transferred to the transfer material without passing through the intermediate transfer member.

  The first mode is a full-color mode that uses the toner image formed on all of the plurality of image carriers, and the second mode is one image carrier among the plurality of image carriers. It is preferable that the monochrome mode uses the formed toner image.

According to a third aspect of the present invention, an image forming apparatus includes:
Transfer means for transferring a toner image to an intermediate transfer member or a transfer material, and forming an image on the intermediate transfer member or the transfer material;
Selection means for selecting one mode from a plurality of modes including a first mode for forming the image using a plurality of colors and a second mode for forming the image using fewer colors than the first mode. When,
The transfer rate of the toner image in the second mode is larger than the transfer rate of the toner image in the first mode when the toner image is transferred onto the intermediate transfer member or the transfer material by the transfer unit. And a control means for controlling the transfer means.

  In the second mode, it is preferable to form the image using one color.

The image forming apparatus includes a plurality of image carriers on which the toner images of different colors are formed,
The transfer unit transfers the toner image formed on the image carrier onto the intermediate transfer member or the transfer material by bringing the intermediate transfer member or the transfer material into contact with the image carrier. ,
In the second mode, among the plurality of image carriers, the image carrier on which no toner image is formed is preferably separated from the intermediate transfer member or the transfer material.

  Preferably, the control unit controls a transfer rate of the toner image by controlling a current value or a voltage value of the transfer unit.

  When the intermediate transfer member is provided, the intermediate transfer member preferably has an endless belt shape.

  The image forming apparatus preferably includes an endless belt-shaped conveying unit that conveys the transfer material when the toner image is directly transferred to the transfer material without passing through the intermediate transfer member.

  The first mode is a full-color mode that uses the toner image formed on all of the plurality of image carriers, and the second mode is one image carrier among the plurality of image carriers. It is preferable that the monochrome mode uses the formed toner image.

According to a fourth aspect of the present invention, an image forming apparatus includes:
Transfer means for transferring a toner image to an intermediate transfer member or a transfer material, and forming an image on the intermediate transfer member or the transfer material;
A plurality of modes including a first mode in which the image is formed using a plurality of colors including a first color and a second mode in which the image is formed using less colors than the first mode including the first color. Selecting means for selecting one mode from the modes;
The output value for transferring the first color toner image in the first mode when the toner image is transferred onto the intermediate transfer member or the transfer material by the transfer unit is greater than the second output value. And a control unit for controlling the transfer unit so that an output value for transferring the toner image of the first color in the mode is increased.

  In the second mode, it is preferable to form the image using one color.

The image forming apparatus includes a plurality of image carriers on which the toner images of different colors are formed,
The transfer unit transfers the toner image formed on the image carrier onto the intermediate transfer member or the transfer material by bringing the intermediate transfer member or the transfer material into contact with the image carrier. ,
In the second mode, among the plurality of image carriers, the image carrier on which no toner image is formed is preferably separated from the intermediate transfer member or the transfer material.

  Preferably, the control means controls the output value of the transfer means by controlling the current value or voltage value of the transfer means.

  When the intermediate transfer member is provided, the intermediate transfer member preferably has an endless belt shape.

  The image forming apparatus preferably includes an endless belt-shaped conveying unit that conveys the transfer material when the toner image is directly transferred to the transfer material without passing through the intermediate transfer member.

  The first mode is a full-color mode that uses the toner image formed on all of the plurality of image carriers, and the second mode is one image carrier among the plurality of image carriers. It is preferable that the monochrome mode uses the formed toner image.

According to a fifth aspect of the present invention, an image forming apparatus includes:
A plurality of image carriers on which toner images of different colors are formed;
A transfer unit comprising a plurality of transfer means provided corresponding to each of the plurality of image carriers in order to transfer the toner image formed on the image carrier to an intermediate transfer member or a transfer material;
Control means for controlling the output value of each of the plurality of transfer means,
The control means forms the toner image only on a part of the plurality of image carriers, and then transfers the toner image to the intermediate transfer member or transfer material. The output value of the transfer means provided for the image carrier other than the image carrier is smaller than the output value of the transfer means provided for the part of the image carriers. The transfer unit is controlled.

  The control means forms the toner image only on a part of the plurality of image carriers, and then transfers the toner image to the intermediate transfer member or transfer material. The output value of the transfer means provided for an image carrier other than the image carrier is ½ or less of the output value of the transfer means provided for the part of the image carriers. It is preferable to control the transfer portion.

  The control means forms the toner image only on a part of the plurality of image carriers, and then transfers the toner image to the intermediate transfer member or transfer material. An output value of the transfer means provided for an image carrier other than the image carrier is ½ or less of an output value of the transfer means provided for the part of the image carriers, In addition, it is preferable to control the transfer portion so as to be larger than zero.

  When the toner image is formed only on a part of the plurality of image carriers, and then the toner image is transferred to the intermediate transfer member or the transfer material, the plurality of image carriers and the intermediate It is preferable to contact the transfer body or the transfer material.

  When the intermediate transfer member is provided, the intermediate transfer member preferably has an endless belt shape.

The image forming apparatus includes an endless belt-shaped transport unit that transports the transfer material,
The transfer unit preferably transfers the toner images formed on the plurality of image carriers onto the transfer material conveyed by the conveying unit.

  It is preferable that the number of the image bearing members is one or two.

  Preferably, the control unit controls the output value by controlling a current value or a voltage value of the transfer unit.

In addition, the image forming apparatus on each side described above is
Toner images of different colors are formed on a plurality of image carriers, and the formed toner images are transferred onto an endless belt-like intermediate transfer member or a transfer material conveyed with the endless belt-like intermediate transfer member. In the image forming apparatus capable of mode switching between a full color mode for forming an image and a subtractive color mode for forming an image using only a part of the plurality of image carriers. Regarding the output value of each transfer means for transferring from the carrier to the endless belt-shaped intermediate transfer body or the transfer material, only the toner image of the color required in the subtractive color mode than the output value of all the transfer means in the full color mode. It is preferable to increase the output value of the transfer means used for transfer.

  Further, it is preferable that one image carrier is used in the color reduction mode.

  Further, it is preferable that an image carrier not used in the color reduction mode does not contact the endless belt-shaped intermediate transfer body or the transfer material.

  Then, toner images of different colors are formed on a plurality of image carriers, and the formed toner images are transferred onto the endless belt-shaped intermediate transfer member or a transfer material conveyed together with the endless belt-shaped intermediate transfer member. An image forming apparatus for forming a transfer image between a full color mode using all the different color toners and a subtractive color mode using a part of the different color toners. In an image forming apparatus capable of mode switching, in the subtractive color mode, when the output value of the transfer means for transferring from the image carrier corresponding to the color toner to be used is 1, the image carrier corresponding to the unused color toner It is preferable to set the output value of the transfer means for transferring from the body to half or less including zero.

  In the color reduction mode, it is preferable that all the image carriers and the endless belt-shaped intermediate transfer body or the transfer material are in contact with each other.

  In the color reduction mode, it is preferable to use one or two color toners.

  According to the present invention, it is possible to stably form a full-color image and a monochrome image using a subtractive color toner with a plurality of colors of toner. Further, it is possible to prevent the occurrence of an image defect in the image forming apparatus that can switch between the full color mode and the color reduction mode. In particular, the transfer rate can be prevented from being lowered, and the toner can be recycled to the image carrier on the downstream side. The functions of preventing transfer and preventing peeling discharge in the transfer region between the endless belt-shaped intermediate transfer member and the image carrier can be stably and reliably achieved.

  Embodiments of the present invention will be described below. The description in this column does not limit the technical scope of the claims or the meaning of terms. In addition, the following assertive description in the embodiment of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.

  FIG. 1 is a cross-sectional configuration diagram showing a color image forming apparatus as an embodiment of the image forming apparatus of the present invention.

  This color image forming apparatus is called a tandem type color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, an endless belt-shaped intermediate transfer body unit 7 as a transfer unit, and a transfer material. It has an endless belt-shaped paper feeding / conveying means 21 for conveying P and a belt-type fixing device 24 as a fixing means. A document image reading device SC is disposed on the upper part of the main body A of the image forming apparatus.

  As one of the different color toner images formed on each photoconductor, an image forming unit 10Y that forms a yellow image includes a drum-shaped photoconductor 1Y as a first image carrier, and the photoconductor 1Y. A charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, a primary transfer roller 5Y as a primary transfer unit, and a cleaning unit 6Y are arranged around the periphery. In addition, an image forming unit 10M that forms a magenta image as another different color toner image is a drum-shaped photoconductor 1M as a first image carrier, and is arranged around the photoconductor 1M. The charging unit 2M, the exposure unit 3M, the developing unit 4M, the primary transfer roller 5M as the primary transfer unit, and the cleaning unit 6M are included. In addition, an image forming unit 10C that forms a cyan image as another different color toner image includes a drum-shaped photoconductor 1C as a first image carrier, and around the photoconductor 1C. A charging unit 2C, an exposure unit 3C, a developing unit 4C, a primary transfer roller 5C as a primary transfer unit, and a cleaning unit 6C are disposed. In addition, an image forming unit 10K that forms a black image as one of other different color toner images is disposed around a drum-shaped photoconductor 1K as a first image carrier and the photoconductor 1K. A charging unit 2K, an exposure unit 3K, a developing unit 4K, a primary transfer roller 5K as a primary transfer unit, and a cleaning unit 6K.

  The endless belt-like intermediate transfer body unit 7 includes an endless belt-like intermediate transfer body 70 as a second image carrier having a semiconductive endless belt shape that is wound around a plurality of rollers and is rotatably supported.

  The images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred and synthesized on the rotating endless belt-shaped intermediate transfer body 70 by the primary transfer rollers 5Y, 5M, 5C, and 5K. A color image is formed. A transfer material P such as a sheet as a recording medium accommodated in the sheet feeding cassette 20 is fed by a sheet feeding / conveying means 21, passes through a plurality of intermediate rollers 22 A, 22 B, 22 C, 22 D, and a registration roller 23, and then is secondary. The color image is transferred onto the transfer material P at a time by being conveyed to a secondary transfer roller 5A as a transfer means. The transfer material P on which the color image has been transferred is fixed by the belt-type fixing device 24, is sandwiched between the discharge rollers 25, and is placed on the discharge tray 26 outside the apparatus.

  On the other hand, after the color image is transferred to the transfer material P by the secondary transfer roller 5A, the residual toner is removed from the endless belt-shaped intermediate transfer body 70 from which the transfer material P is separated by the curvature by the cleaning means 6A.

  During the image forming process, the primary transfer roller 5K is always in pressure contact with the photoreceptor 1K. The other primary transfer rollers 5Y, 5M, and 5C are pressed against the corresponding photoreceptors 1Y, 1M, and 1C, respectively, only during color image formation.

  The secondary transfer roller 5A is in pressure contact with the endless belt-shaped intermediate transfer body 70 only when the transfer material P passes through the secondary transfer roller 5A.

  Further, the housing 8 can be pulled out from the apparatus main body A through the support rails 82L and 82R.

  The housing 8 includes image forming units 10Y, 10M, 10C, and 10K, and an endless belt-shaped intermediate transfer body unit 7.

  The image forming units 10Y, 10M, 10C, and 10K are arranged in tandem in the vertical direction. An endless belt-shaped intermediate transfer body unit 7 is disposed on the left side of the photoreceptors 1Y, 1M, 1C, and 1K in the figure. The endless belt-shaped intermediate transfer body unit 7 includes an endless belt-shaped intermediate transfer body 70 that can be rotated by winding rollers 71, 72, 73, 74, and 76, primary transfer rollers 5Y, 5M, 5C, and 5K, and cleaning means 6A. It consists of.

  The image forming units 10Y, 10M, 10C, and 10K and the endless belt-shaped intermediate transfer body unit 7 are integrally pulled out from the main body A by the drawer operation of the housing 8.

  In this way, a toner image is formed on the photoreceptors 1Y, 1M, 1C, and 1K by charging, exposing, and developing, and the toner images of each color are superimposed on the endless belt-shaped intermediate transfer body 70, and are collectively applied to the transfer material P. The image is transferred and fixed by a belt-type fixing device 24 by pressing and heating. The photoreceptors 1Y, 1M, 1C, and 1K after transferring the toner image to the transfer material P are cleaned by the cleaning device 6A after the toner remaining on the photoreceptor is transferred, and then the above-described charging, exposure, and development cycle. The next image formation is performed.

The process speed of this image forming apparatus is 220 mm / s when A4 size is used, the primary transfer roller is a sponge roller having a resistance value of 1 × 10 ⁷ Ω and a diameter of 20 mm, and transfer control is constant voltage control. In the full color mode, as shown in the cross-sectional configuration diagram of FIG. 1 and the schematic diagram of FIG. 2, the photoreceptors 1Y, 1M, 1C, and 1K are respectively connected to the primary transfer rollers 5Y, 5M, Although the base 5T of 5C and 5K slides in the guide 5G by the pin D and moves in the direction of the arrow A, the spring S acts and is pressed by the primary transfer rollers 5Y, 5M, 5C and 5K. In the monochrome mode, which is the monochrome mode, only the black photosensitive member 1K is pressed against the black primary transfer roller 5K through the endless belt-shaped intermediate transfer member 70 as shown in the schematic diagram of FIG. C In this case, by moving the base 5T of each primary transfer roller 5Y, 5M, 5C in the direction of the arrow B by the pin D, each photoreceptor 1Y, 1M, 1C, the endless belt-shaped intermediate transfer body 70, and each primary transfer. Contact and pressing with the rollers 5Y, 5M, and 5C are released.

  Note that the tension switching of the endless belt-shaped intermediate transfer body 70 in switching between the full color mode and the monochrome mode is performed by sliding the tension adjuster 9 shown in FIGS. 1, 2, and 3 in the ± C direction. The tension adjuster 9 is configured such that, for example, a base 9A equipped with rollers 76 and 77 can be slid and moved on a guide 9B by a pin D.

  Plotting the transfer rate of each toner image against the change of the primary transfer current in the full color mode and the monochrome mode results in the graphs of FIGS.

  In the full color mode, as shown in FIG. 4, the transfer rate is about 90% at a peak when Y is a transfer current of 25 μA, and the transfer rate is about 92% at a peak when M is a transfer current of 29 μA. In C, the transfer rate is about 94% at a peak when the transfer current is 32 μA, and in K, the transfer rate is about 96% at a peak when the transfer current is 35 μA. All colors have the same level and high transfer rate when the transfer current is 25 μA and the transfer rate is 90%.

  At the time of monochrome as shown in FIG. 3, the graph of FIG. 5 is the same as the curve of K shown in the graph of FIG. 4. When the transfer current is 35 μA, the transfer rate reaches a peak of approximately 96%.

  Therefore, the transfer rate of the black toner image in the monochrome mode to the endless belt-like intermediate transfer member 70 is set to be larger than the transfer rate of the black toner image to the endless belt-like intermediate transfer member in the full color mode. It is preferable to control the endless belt-shaped intermediate transfer body unit 7.

  Thus, in the second mode such as the monochrome mode, which is a mode for forming an image using fewer colors than the first mode for forming an image using a plurality of colors such as full color, at least in the second mode. By controlling the endless belt-shaped intermediate transfer body unit 7 so that the transfer rate of the toner image of each color is larger than the transfer rate of the toner image of that color in the first mode, retransfer of the toner is prevented, A good transfer rate can be obtained in the second mode.

  Furthermore, it is more preferable to control the transfer rate of each toner image in the first mode so as to be smaller than the transfer rate of each color toner image in the second mode. The transfer rate can be achieved by controlling the current value or voltage value of each primary transfer roller 5Y, 5M, 5C, 5K of the endless belt-like intermediate transfer body unit 7 which is a transfer means.

  In this case, at least the current value or the voltage value of the primary transfer roller (5K in the present embodiment) corresponding to the photoconductor (1K in the present embodiment) on which the toner image is formed in the second mode is greater than that in the first mode. It is preferable to control so as to increase in the second mode.

  Further, the current values or voltage values of all the primary transfer rollers 5Y, 5M, 5C, and 5K in the first mode are set in the second mode of the primary transfer roller corresponding to the photoconductor on which the toner image is formed in the second mode. It is preferable to control so that it may become smaller than a current value or a voltage value.

  FIG. 6 is a block diagram showing a main control portion for performing the above-described control. As shown in FIG. 6, the image forming apparatus 1 includes a CPU 61 that transmits a control signal to each drive unit. The CPU 61 drives the pins D of the primary transfer rollers 5Y, 5M, 5C, and 5K, and the photosensitive members 1Y, 1M, 1C, and 1K, the endless belt-shaped intermediate transfer body 70, and the primary transfer rollers 5Y and 5M. , 5C, and 5K are electrically connected to each other. Further, the CPU 61 includes a transfer power source 63 that supplies power to the primary transfer rollers 5Y, 5M, 5C, and 5K at the time of transfer, a counter 64 that counts the number of formed images, and a temperature / humidity detector 65 that detects temperature and humidity. A printing rate data table storage unit 66 that stores a printing rate data table for converting the image data so as to correspond to each mode, and each primary transfer roller set to have a transfer rate corresponding to each mode. A transfer table storage unit 67 that stores current values or voltage values of 5Y, 5M, 5C, and 5K is electrically connected. The CPU 61, the cam motor 62, the transfer power source 63, the counter 64, the temperature / humidity detection unit 65, the printing rate data table storage unit 66, and the transfer table storage unit 67 are the control means of the present invention.

  The CPU 61 is electrically connected to an operation unit 68 for inputting various instructions such as an image formation start mode and an image formation mode.

  The CPU 61 recognizes the mode (full color, monochrome, single color (R, G, B, Y, M, C)) input from the operation unit 68 as selection means, and the cam motor 62 according to the selected mode. As shown in FIG. 3, the contact and non-contact states of the photoreceptors 1Y, 1M, 1C, and 1K and the endless belt-shaped intermediate transfer member 70 are switched according to the selected mode.

  Further, the CPU 61 converts the image data according to the selected mode based on the printing rate data table stored in the printing rate data table storage unit 66. Further, the CPU 61 sets each of the primary transfer rollers 5Y, 5M, 5C, and 5K from the transfer table stored in the transfer table storage unit 67 according to the selected mode so that the transfer rate corresponds to the mode. Read current value or voltage value. At this time, the CPU 61 corrects the current value or the voltage value according to the detection result of the temperature / humidity detection unit 65 and sets the transfer rate suitable for the environment.

  When the toner image based on the above-described printing rate data table is formed on each of the photoreceptors 1Y, 1M, 1C, and 1K, the CPU 61 controls the transfer power source 63 based on the corrected current value or voltage value, The transfer rate of each primary transfer roller 5Y, 5M, 5C, 5K is controlled. As a result, each toner image is transferred to the belt-shaped intermediate transfer body 70.

  Specifically, when the transfer rate is controlled by the current value, when the full color mode is selected, the CPU 61 transfers the transfer power supply so that the current values of all the primary transfer rollers 5Y, 5M, 5C, and 5K are 25 μA. 63 is controlled. On the other hand, when the monochrome mode is selected, the CPU 61 sets the transfer power supply 63 so that only the current value of the black primary transfer roller 5K is 35 μA and the current values of the other primary transfer rollers 5Y, 5M, and 5C are 5 μA. Control.

  Next, in both the full color mode and the subtractive color mode including monochrome, each photoconductor is pressed against each primary transfer roller via an endless belt-shaped intermediate transfer body as shown in FIGS. Describe the case.

The process speed of this image forming apparatus is 220 mm / s when A4 size is used, the primary transfer roller is a sponge roller having a resistance value of 1 × 10 ⁷ Ω and a diameter of 20 mm, and transfer control is constant voltage control. .

  The full color mode is as described above, but each of the primary colors Y, M, C, and K for forming a red toner image, which is a combined monochrome of Y and M, as a monochrome (monochrome) mode of the subtractive color mode. Table 1 was obtained by checking the state of the peeling discharge and the value of the transfer rate by changing the transfer current of the transfer roller.

  Here, ◯ indicates no occurrence of peeling discharge, Δ indicates occurrence that is not practically considered, and × indicates that the transferred image is disturbed and cannot be used practically.

  If the primary transfer current of Y and M used for red composition is 25 μA, and the other two (C and K) primary transfer currents are both 5 μA, 10 μA, or 0, it is very good for avoiding peeling discharge. It can be seen that the rate is also very high.

  The output value of the transfer means for transferring from the photoconductor corresponding to the unused color toner is less than half of the output value including 0, more than the output value 25 μA of the transfer means for transferring from the photoconductor corresponding to the color toner to be used. It can be seen that the case of 10 μA, 5 μA, and 0 μA is very good for improving the state of inhibiting the stripping discharge and the transfer rate. In particular, the transfer current of 5 μA is optimal from the viewpoint of transfer rate.

  Further, it is preferable that the output value of the transfer means for transferring from the photoconductor corresponding to the unused color toner is larger than zero. By doing so, it is possible to prevent the toner image from being disturbed when the transferred toner image on the endless belt-shaped intermediate transfer body 70 passes the position of the transfer means corresponding to the toner of the unused color. it can.

  Incidentally, referring to the above results, combinations of photoreceptors used to create color images of single colors of Y, M, C, K, red (R), blue (B), and green (G), and their use Table 2 shows the optimum values of transfer currents applied to the primary transfer rollers of all the photoreceptors including the photoreceptors other than the photoreceptors. Here, the required colors in Table 2 indicate each mode.

  In order to create each single color image, for example, a transfer table as shown in Table 2 is stored in advance in the transfer table storage unit 67. When the monochrome color mode is selected from the operation unit 68, the CPU 61 converts the image data to correspond to the selected mode based on the printing rate data table stored in the printing rate data table storage unit 66. To do. The CPU 61 then selects the primary transfer rollers 5Y, 5M, 5C from the transfer table in Table 2 stored in the transfer table storage unit 67 according to the selected mode so that the transfer rate corresponds to the mode. , 5K current value or voltage value is read. For example, in the mode in which the desired color is Y, only the current value of the primary transfer roller 5Y of Y is 25 μA, and the current values of the other primary transfer rollers 5M, 5C, 5K are 5 μA. In the mode in which the required color is M, only the current value of the primary transfer roller 5M of M is 25 μA, and the current values of the other primary transfer rollers 5Y, 5C, and 5K are 5 μA. In the mode where the desired color is C, only the current value of the primary transfer roller 5C of C is set to 25 μA, and the current values of the other primary transfer rollers 5Y, 5M, and 5K are set to 5 μA. In the mode in which the desired color is red, only the current values of the primary transfer rollers 5Y and 5M of Y and M are set to 25 μA, and the current values of the other primary transfer rollers 5C and 5K are set to 5 μA. In the mode where the required color is blue, only the current values of the primary transfer rollers 5M and 5C of M and C are set to 25 μA, and the current values of the other primary transfer rollers 5Y and 5K are set to 5 μA. In the mode where the required color is green, only the current values of the primary transfer rollers 5Y and 5C of Y and C are set to 25 μA, and the current values of the other primary transfer rollers 5M and 5K are set to 5 μA.

  As described above, it has become possible to stably form a full-color image and a monochrome image using a subtractive color toner with a plurality of colors of toner. Further, it is possible to prevent the occurrence of an image defect in the image forming apparatus that can switch between the full color mode and the color reduction mode. In particular, the transfer rate can be prevented from being lowered, and the toner can be recycled to the image carrier on the downstream side. The functions of preventing transfer and preventing peeling discharge in the transfer region between the endless belt-shaped intermediate transfer member and the image carrier can be stably and reliably achieved.

  In the present embodiment, the first mode is a full color mode that forms an image using a plurality of colors, and the second mode is a monochrome mode that forms an image using fewer colors than the first mode. The difference between the first mode and the second mode is not limited to this.

  For example, the first mode is a mode in which an image is formed using a plurality of colors including the first color, and the second mode is formed using an image including the first color and fewer colors than the first mode. It is good also as a mode. In such a case, it is preferable that the transfer rate of the first color toner image in the second mode be larger than the transfer rate of the first color toner image in the first mode. Specifically, a mode in which the required color is Y and a mode in which the color is red will be described as an example. Since the Y color is used in both modes, Y is the first color only in these two modes. It becomes. Further, depending on the total number of colors used, the mode in which the required color is red is the first mode, and the mode in which the required color is Y is the second mode. In other words, if the Y transfer rate in the mode in which the required color is Y is set larger than the Y transfer rate in the mode in which the required color is red, the image quality can be formed more stably. .

  Further, the first mode may be a mode for forming an image using a first number of colors, and the second mode may be a mode for forming an image using a number of colors smaller than the first number. In such a case, it is preferable that the transfer rate of the toner image in the second mode is larger than the transfer rate of the toner image in the first mode for at least one color used in the second mode. Specifically, a mode in which the required color is C and a mode in which the red color is used will be described as an example. Based on the total number of colors used, the mode in which the required color is red is the first mode, and the mode in which the required color is C. Becomes the second mode. In other words, if the C transfer rate in the mode in which the required color is C is set larger than the Y and M transfer rates in the mode in which the required color is red, the image quality can be formed more stably. It becomes.

1 is a cross-sectional configuration diagram illustrating a color image forming apparatus as an embodiment of an image forming apparatus of the present invention. FIG. 3 is a schematic diagram illustrating an arrangement of a photoconductor and a primary transfer unit when full color image formation is performed in a color image forming apparatus as an embodiment of the image forming apparatus of the present invention. FIG. 2 is a schematic diagram illustrating an arrangement of a photoconductor and a primary transfer unit when a black image is formed in a color image forming apparatus as an embodiment of the image forming apparatus of the present invention. 5 is a graph showing a relationship between a transfer current value by each primary transfer roller in a full color mode and a transfer rate from each photoconductor to an endless belt-shaped intermediate transfer body or transfer material. 7 is a graph showing a relationship between a transfer current value by a primary transfer roller in a black (K) mode and a transfer rate from a black photosensitive member to an endless belt-shaped intermediate transfer member or a transfer material. FIG. 3 is a block diagram showing a main control portion in a color image forming apparatus as an embodiment of the image forming apparatus of the present invention.

Explanation of symbols

1Y, 1M, 1C, 1K Photoconductors 4Y, 4M, 4C, 4K Developing means 5Y, 5M, 5C, 5K Primary transfer roller as primary transfer means 5A Secondary transfer roller as secondary transfer means 6Y, 6M, 6C, 6K Cleaning means 7 Endless belt-shaped intermediate transfer body unit 24 Belt-type fixing device 61 CPU
62 Cam Motor 63 Transfer Power Supply 64 Counter 65 Temperature Humidity Detection Unit 67 Transfer Table Storage Unit 68 Operation Unit

Claims (19)

Transfer means for transferring a toner image to an intermediate transfer member or a transfer material, and forming an image on the intermediate transfer member or the transfer material;
A plurality of modes including a first mode in which the image is formed using a plurality of colors including a first color and a second mode in which the image is formed using less colors than the first mode including the first color. Selecting means for selecting one mode from the modes;
The transfer rate of the toner image of the first color in the first mode when the toner image is transferred onto the intermediate transfer member or the transfer material by the transfer unit is greater than the transfer rate of the first color toner image in the second mode. An image forming apparatus comprising: a control unit configured to control the transfer unit so that a transfer rate of a toner image of one color is increased. Transfer means for transferring a toner image to an intermediate transfer member or a transfer material, and forming an image on the intermediate transfer member or the transfer material;
One mode is selected from a plurality of modes including a first mode in which the image is formed using a first number of colors and a second mode in which the image is formed using a smaller number of colors than the first number. A selection means for selecting;
When at least one color used in the second mode when the toner image is transferred onto the intermediate transfer member or the transfer material by the transfer unit, the transfer rate of the toner image in the first mode is higher than the transfer rate of the toner image in the first mode. An image forming apparatus comprising: a control unit configured to control the transfer unit so that a transfer rate of the toner image in the second mode is increased. Transfer means for transferring a toner image to an intermediate transfer member or a transfer material, and forming an image on the intermediate transfer member or the transfer material;
Selection means for selecting one mode from a plurality of modes including a first mode for forming the image using a plurality of colors and a second mode for forming the image using fewer colors than the first mode. When,
The transfer rate of the toner image in the second mode is larger than the transfer rate of the toner image in the first mode when the toner image is transferred onto the intermediate transfer member or the transfer material by the transfer unit. As described above, the image forming apparatus includes a control unit for controlling the transfer unit. Transfer means for transferring a toner image to an intermediate transfer member or a transfer material, and forming an image on the intermediate transfer member or the transfer material;
A plurality of modes including a first mode in which the image is formed using a plurality of colors including a first color and a second mode in which the image is formed using less colors than the first mode including the first color. Selecting means for selecting one mode from the modes;
The output value for transferring the first color toner image in the first mode when the toner image is transferred onto the intermediate transfer member or the transfer material by the transfer unit is greater than the second output value. An image forming apparatus comprising: a control unit for controlling the transfer unit so that an output value for transferring the toner image of the first color in the mode is increased. The image forming apparatus according to claim 1, wherein the image is formed using one color in the second mode. The image forming apparatus includes a plurality of image carriers on which the toner images of different colors are formed,
The transfer unit transfers the toner image formed on the image carrier onto the intermediate transfer member or the transfer material by bringing the intermediate transfer member or the transfer material into contact with the image carrier. ,
5. The image bearing member in which a toner image is not formed among the plurality of image bearing members in the second mode is separated from the intermediate transfer member or the transfer material. The image forming apparatus according to claim 1. The image forming apparatus according to claim 1, wherein the control unit controls a transfer rate of the toner image by controlling a current value or a voltage value of the transfer unit. The image forming apparatus according to claim 4, wherein the control unit controls an output value for transferring the toner image by controlling a current value or a voltage value of the transfer unit. The image forming apparatus according to claim 1, wherein the intermediate transfer member has an endless belt shape when the intermediate transfer member is included. The image forming apparatus according to claim 1, further comprising an endless belt-shaped transport unit that transports the transfer material to a transfer position. The first mode is a full color mode that uses the toner image formed on all of the plurality of image carriers, and the second mode is formed on one image carrier among the plurality of image carriers. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is a single color mode using the toner image. A plurality of image carriers on which toner images of different colors are formed;
A transfer unit comprising a plurality of transfer means provided corresponding to each of the plurality of image carriers in order to transfer the toner image formed on the image carrier to an intermediate transfer member or a transfer material;
Control means for controlling the output value of each of the plurality of transfer means,
The control means forms the toner image only on a part of the plurality of image carriers, and then transfers the toner image to the intermediate transfer member or transfer material. The output value of the transfer means provided for the image carrier other than the image carrier is smaller than the output value of the transfer means provided for the part of the image carriers. An image forming apparatus that controls the transfer unit. The control means forms the toner image only on a part of the plurality of image carriers, and then transfers the toner image to the intermediate transfer member or transfer material. The output value of the transfer means provided for an image carrier other than the image carrier is ½ or less of the output value of the transfer means provided for the part of the image carriers. The image forming apparatus according to claim 12, wherein the transfer unit is controlled. The control means forms the toner image only on a part of the plurality of image carriers, and then transfers the toner image to the intermediate transfer member or transfer material. An output value of the transfer means provided for an image carrier other than the image carrier is ½ or less of an output value of the transfer means provided for the part of the image carriers, The image forming apparatus according to claim 12, wherein the transfer unit is controlled to be larger than zero. When the toner image is formed only on a part of the plurality of image carriers, and then the toner image is transferred to the intermediate transfer member or the transfer material, the plurality of image carriers and the intermediate The image forming apparatus according to claim 12, wherein the image forming apparatus is in contact with a transfer body or the transfer material. The image forming apparatus according to claim 12, wherein the intermediate transfer member has an endless belt shape when the intermediate transfer member is included. When having an endless belt-shaped transport means for transporting the transfer material to the transfer position of the image carrier,
The image forming apparatus according to claim 12, wherein the transfer unit transfers the toner images formed on the plurality of image carriers to the transfer material conveyed by the conveying unit. The image forming apparatus according to claim 12, wherein the number of the image bearing members is one or two. The image forming apparatus according to claim 12, wherein the control unit controls the output value by controlling a current value or a voltage value of the transfer unit.

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