JP2009157041A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To output both images of an image which is prevented from "mixing of colors in a high toner attachment image in normal developing" and an image which is prevented from "deterioration of reproducing property for highlight in normal developing", in an image forming apparatus obtaining a good toner adhesion quantity by using a method of superposing color on an image carrier. <P>SOLUTION: At least one developing unit 4 which is after a second color in a printer obtaining a superposed color image by sequentially forming toner images for each color on a photoreceptor is a normal developing means for developing an unexposed section by the toner which is charged to a reverse polarity as the charging polarity of the photoreceptor. Developing bias applied to toner carrier 42 of the normal developing means is composed to be variable. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer. More specifically, the present invention relates to an image forming apparatus that forms a color image by superimposing a plurality of color toner images on one image carrier.

  As the image forming apparatus, there is known a color superimposing method on a photoconductor (so-called IOI (Image on Image) method) in which a plurality of colors are sequentially developed and superimposed on one photoconductor, and then collectively transferred. (For example, Patent Document 1). This color superimposing method on the photoreceptor has the advantage that only one photoreceptor is required, and is a technology that can save resources, save space, and reduce costs.

  In the image forming apparatus using the color superimposing method on the photoreceptor described in Patent Document 1, a latent image is obtained by exposing the image portion on the surface of the photoreceptor uniformly charged by the charging means to attenuate the potential. Then, an image forming process for developing the latent image with a toner having the same polarity as the charged polarity of the surface of the photoconductor is performed for each color to form a color toner image in which the toner images of the respective colors are superimposed on the photoconductor. That is, the photosensitive member is charged and exposed to form an electrostatic latent image of the first color, and developed by attaching toner to the exposed portion. Then, in order to form toner images for the second and subsequent colors, an electrostatic latent image is formed by charging and exposing the photosensitive member on which the toner image has already been formed, and the toner image is attached to the exposed portion. The development process is repeated.

  However, in the development for the second and subsequent colors, there has been a problem that the amount of toner developed (toner adhesion amount) differs greatly between the region where the toner image is present on the photoreceptor and the region where there is no toner image. The reasons for this are as follows: 1. The written laser beam is absorbed by the already formed toner image (the potential increases after exposure). It can be mentioned that the post-exposure potential does not decrease (increased post-exposure potential) in the same manner as in a region where there is no toner image, depending on the amount of charge of the already formed toner image. As described above, in the image forming process steps for the second and subsequent colors, the post-exposure potential in the area where the toner image already exists increases, and the development potential which is the difference between the post-exposure potential and the development bias in the area where there is no toner image. As a result, the amount of toner varies.

  In order to solve this problem, Japanese Patent Application Laid-Open No. H10-228667 changes the writing conditions such as the laser beam emission amount and the beam diameter so as to correct the influence on the post-exposure potential caused by the toner already formed on the photoreceptor. What to do has been proposed. However, in the method of performing correction by changing the writing condition in this way, it is necessary that the writing positions between different colors are exactly the same, and in a high resolution such as 600 dpi and 1200 dpi recently desired, It is extremely difficult to accurately match the writing positions.

Japanese Patent No. 3014168

  In order to solve the above problems, the present applicant has proposed an image forming apparatus that uses regular development in a color superimposing method on a photoreceptor in Japanese Patent Application No. 2007-055998 (hereinafter referred to as “prior application”). Specifically, in the image forming apparatus of the prior application, a latent image is formed by exposing a non-image portion on the surface of the photoreceptor uniformly charged by the charging means to attenuate the potential, and the latent image is exposed to light. An image forming process for forming a toner image by developing with a toner having a polarity opposite to the charged polarity on the surface of the body is performed for each color to form a color toner image in which the toner images of the respective colors are superimposed on the photoreceptor. As a result, the first color toner image formed on the photoconductor is charged together with the photoconductor by the charging means with a polarity opposite to the original toner charge polarity when the second color image forming process is performed. As a result, when the photosensitive member is charged to a predetermined potential (the same potential as that of the first color) by the charging means, the toner image of the first color is also removed. That is, when the second color latent image is developed by discharging the first color toner image and reducing the potential by charging the second color, there is no portion where the first color toner image is present in the second color latent image. The development potential, which is the difference between the charging potential and the development bias, is approximately the same between the portions, and a toner image of the second color can be formed without causing uneven toner density. Needless to say, when two or more color toner images are formed, the next color toner image can be formed without being affected by the potential of the previous color toner image.

  However, in the normal development, the development potential is substantially the same in the portion where the toner image of the first color in the latent image of the second color is present and in the portion where the toner image is not present. The background potential, which is the difference, will change. That is, in regular development, if the post-exposure potential increases in a portion where the toner image of the first color is present, there is a problem that the background potential is not sufficiently obtained and the toner adheres to an area where the toner is not desired to be adhered. Specifically, when an image in which a large amount of toner is attached to the first color, such as a solid image, the post-exposure potential of the second color increases even if the second color is a background portion. For this reason, in the second color, the background potential cannot be sufficiently obtained, and the toner adheres slightly, causing a problem that the solid image of the first color cannot be reproduced without color mixing. In addition, this problem becomes more serious under the circumstances where the first color is solid and the second color is solid, and unintended toner tends to adhere to the third color and the fourth color (hereinafter, this problem is referred to as “regular This will be referred to as “color mixing with a high toner adhesion image in development”).

  In addition, if the development bias is set so that the background potential is sufficiently large for the purpose of preventing this “color mixing in a high toner adhesion image in regular development”, the development potential cannot be sufficiently large contrary. This causes a problem that highlights (low density images) cannot be reproduced well (hereinafter, this problem will be referred to as “deterioration of highlight reproducibility in regular development”).

  The present invention has been made in view of the above background, and the object of the present invention is that a toner image has already been formed by using a method of forming a color image by superposing a toner image on an image carrier. In an image forming apparatus that obtains a good toner adhesion amount even when a toner image is formed on an image carrier, an image in which “color mixture with a high toner adhesion image in regular development” is prevented, and “highlight reproducibility in regular development” Provided is an image forming apparatus capable of outputting both an image and an image in which “deterioration” is prevented.

In order to achieve the above object, the invention of claim 1 is directed to exposing an image carrier, a charging unit for charging the image carrier, and the image carrier charged by the charging unit for each color. A latent image forming means for forming a latent image; and a plurality of developing means for visualizing the latent image formed on the image carrier with toners of different colors. In an image forming apparatus that forms a toner image of each color on the image carrier to obtain a superimposed color image by performing charging by the means, latent image formation by the latent image forming means, and development by the developing means.
At least one developing unit that forms a toner image on an image carrier on which a toner image has already been formed among the plurality of developing units is configured to use a toner having a polarity opposite to the charged polarity of the image carrier, It is a normal developing means for developing the exposed portion, and is characterized in that the developing bias of the normal developing means can be changed.
According to a second aspect of the present invention, there is provided an image bearing member, a charging unit for charging the image bearing member, and a latent image for forming a latent image for each color by exposing the image bearing member charged by the charging unit. Forming means, and a plurality of developing means for visualizing the latent image formed on the image carrier with toners of different colors, and charging by the charging means for each color, the latent image Forming a latent image by the forming means and developing by the developing means to sequentially form toner images of respective colors on the image carrier to obtain a superimposed color image;
An image forming apparatus comprising color reproduction characteristic selecting means for selecting a color reproduction characteristic of the color image, and color reproduction condition changing means for changing an image forming condition relating to the color reproduction characteristic based on a selection result of the color reproduction characteristic selecting means In
At least one developing unit that forms a toner image on an image carrier on which a toner image has already been formed among the plurality of developing units is configured to use a toner having a polarity opposite to the charged polarity of the image carrier, It is a normal developing means for developing the exposed portion, and the color reproduction condition changing means changes the developing bias of the normal developing means.
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the regular development means can select two development biases that satisfy | first development bias |> | second development bias |. The color reproduction characteristic selection unit selects whether to give priority to vividness or tonality, and the color reproduction condition changing unit is selected by the color reproduction characteristic selection unit to give priority to the vividness. In this case, the first developing bias is selected, and when the priority is given to gradation, the second developing bias is selected.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first, second, and third aspects, color color separation processing for performing color separation of color image data to be formed into color image data of the plurality of developing means. And a color color separation processing device for performing color separation by each color separation method corresponding to the development bias.
According to a fifth aspect of the present invention, in the image forming apparatus according to the second or third aspect, the image forming apparatus further comprises a color color separation processing device that performs color separation of the color image data to be formed into each color image data of the plurality of developing units. The color color separation processing device performs color separation by a color separation method according to the development bias selected based on whether the vividness selected by the color reproduction characteristic selection unit is given priority or gradation is given priority. It is a feature.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the second, third, fourth, and fifth aspects, the color reproduction characteristic selected by the color reproduction characteristic selection unit is selected based on a user instruction. It is characterized by being.
According to a seventh aspect of the present invention, in the image forming apparatus according to the second, third, fourth, or fifth aspect, the color reproduction characteristic selected by the color reproduction characteristic selection unit is selected based on the color image data to be formed. It is what is made.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first, second, third, fourth, fifth, sixth or seventh aspects, the developing unit faces the image carrier in a non-contact manner in a developing region. And a toner carrier on which the toner is carried in a non-stationary state.
According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect, the toner carrier includes a plurality of electrodes arranged side by side at a predetermined interval, and a power source for applying a multiphase voltage to the electrodes. The toner is carried to a region facing the image carrier while being carried by a traveling wave electric field formed by a voltage applied between a plurality of electrodes by the power source. .
According to a tenth aspect of the present invention, in the image forming apparatus according to the eighth aspect, the toner carrier includes a plurality of electrodes arranged side by side at a predetermined interval, and a power source for applying a multiphase voltage to the electrodes. And the surface of the toner carrier is movable, and the traveling wave electric field formed by the voltage applied between the plurality of electrodes by the power source and the movement of the surface of the toner carrier are arranged on the toner carrier. The toner is conveyed to a region facing the image carrier.
The invention according to claim 11 is the image forming apparatus according to claim 8, wherein the toner carrier includes a plurality of electrodes arranged side by side at a predetermined interval, and a power source for applying a voltage to the electrodes. The surface of the toner carrier is movable, and the toner is supported in a non-stationary state by an oscillating electric field formed by a voltage applied between a plurality of electrodes by the power source, and the toner is moved by moving the surface of the toner carrier. The toner on the carrier is transported to a region facing the image carrier.
According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, or eleventh aspects, each of the plurality of developing units is cyan. Development is performed using toners of four colors, magenta, yellow, and black.

  In the present invention, a normal developing means is used when forming a toner image on an image carrier on which a toner image has already been formed by a method of obtaining a color image by superposing and forming a toner image on the image carrier. In this case, by making it possible to change the development bias of the regular development means, it is possible to cope with both “color mixing with a high toner adhesion image in regular development” and “deterioration of highlight reproducibility in regular development”. For example, if a high toner adhesion image has already been formed on the image carrier and the post-exposure potential rises during the formation of latent images for the second and subsequent colors, the “Color mixing with high toner adhesion image in regular development” For the purpose of prevention, the developing bias is changed so that the background potential, which is the difference between the post-exposure potential and the developing bias, can be increased. On the other hand, for the purpose of preventing "deterioration of highlight reproducibility in regular development", the background potential is reduced, but the development bias is changed so that the development potential, which is the difference between the charging potential and the development bias, can be increased. To do. In this way, by making the development bias changeable, in one image forming apparatus, an image in which “color mixing with a high toner adhesion image in normal development” and “deterioration of highlight reproducibility in normal development” are achieved. An image forming apparatus capable of outputting both an image and an image in which the image is prevented is realized.

  As described above, according to the present invention, when a toner image is formed on an image carrier on which a toner image has already been formed by using a method of forming a color image by superimposing a toner image on the image carrier. In an image forming apparatus that obtains the toner adhesion amount, both an image that prevents “color mixing with a high toner adhesion image in regular development” and an image that prevents “deterioration of highlight reproducibility in regular development” are displayed. There is an excellent effect of being able to output.

Hereinafter, an embodiment in which the present invention is applied to a printer as an image forming apparatus will be described. First, the configuration and operation of the printer according to this embodiment will be described.
FIG. 1 is a schematic configuration diagram of a main part of the printer according to the present embodiment. This printer forms a full-color image by superimposing four color toner images of magenta (M), yellow (Y), cyan (C), and black (K) on a photoconductor as an image carrier. In other words, this is a so-called color superimposing printer. The printer shown in FIG. 1 includes a belt-shaped photoreceptor 1 as an image carrier. From the upstream side to the downstream side along the circumferential direction (arrow direction) of the photosensitive member 1, each of the charging devices (2M, 2Y, 2C, 2K) and the developing devices (4M, 4M, magenta, yellow, cyan, and black) is provided. 4Y, 4C, 4K). Further, on the left side of the apparatus, there is provided a writing device 3 as an exposure device for irradiating the photosensitive member 1 with a laser beam L, and an exposure section (3M, 3Y,...) Between each charging device 2 and each developing device 4 is provided. 3C, 3K) is irradiated with laser light L for forming latent images of the respective colors. That is, as the image forming unit 14 of the printer, a charging device 2M for magenta (M), an exposure unit 3M, a developing device 4M, a charging device 2Y for yellow (Y), an exposure unit 3Y, a developing device 4Y, and cyan (C). Charging device 2C, exposure unit 3C, developing device 4C, black (K) charging device 2K, exposure unit 3K, and developing device 4K are arranged in this order. Around these downstream photoreceptors 1, a pre-transfer charging device 5, a transfer belt device 6 as a transfer device, and a cleaning device 9 are provided. A fixing device 8 is disposed downstream of the transfer belt device 6 with respect to the conveyance direction of the recording paper 7.

  In the charging device 2M for magenta, the photosensitive member 1 is uniformly charged, and the photosensitive member 1 is optically scanned by a laser beam emitted from the writing device 3 from the exposure unit 3M, whereby a magenta electrostatic latent image is formed on the photosensitive member 1. Form an image. The developing device 4 </ b> M develops the magenta electrostatic latent image with magenta toner to form a magenta toner image on the photoreceptor 1. In addition, for three colors of yellow, cyan, and black, toner images are formed on the photoreceptor 1 in the same manner as magenta.

  The superimposed toner image is subjected to charge adjustment by the pre-transfer charging device 5 and then collectively from the photoreceptor 1 to the recording paper 7 as a transfer material (four colors of magenta, yellow, cyan, and black) in the transfer belt device 6. All of the toner images are transferred simultaneously. The toner image transferred onto the recording paper 7 is heat-fixed by the fixing device 8 and becomes an image on the recording paper 7.

  Regarding the charging devices 2Y, 2M, 2C, and 2K, the exposure units 3Y, 3M, 3C, and 3K and the developing devices 4Y, 4M, 4C, and 4K, the parts with the same configuration and operation are subscripts Y, M, C, The explanation is omitted with K omitted.

  The photoreceptor 1 is a so-called single-layer photoreceptor in which a photosensitive layer is coated on a belt-like conductive substrate. The photosensitive layer is formed by dispersing a charge generating material and positive and negative charge transport layers in a polycarbonate resin. Note that the photoconductor 1 used in FIG. 1 belongs to a photoconductor called positively charged OPC in order to impart positive charge. In the printer of this embodiment, the peripheral speed of the photosensitive member 1 is set to 100 mm / sec.

  The charging device 2 is a so-called scorotron charger, and is supplied with a voltage by a power supply device (not shown) provided in the main body of the device, and a grid and a discharge wire held at a predetermined potential with respect to the organic photoreceptor layer of the photoreceptor 1. Charging action is performed by corona discharge caused by. The scorotron charger can apply a uniform potential to the surface of the photoreceptor 1 by controlling the grid voltage. In the printer of this embodiment, the surface of the photoreceptor 1 is uniformly charged to + 700V.

  The writing device 3 has an integrated unit configuration in which laser light L is incident radially on the photosensitive member 1 at four places, and the laser light subjected to light modulation from a laser diode (LD) element is the photosensitive member 1. An optical element is arranged so as to form an image on the surface. By scanning the photoconductor 1 with this laser light, an electrostatic latent image corresponding to a desired image and exposing a non-image portion is formed on the photoconductor. In the printer of this embodiment, the laser diode uses an LD element having a wavelength of 780 nm.

  Although the details of the developing device 4 will be described later, so-called regular development is performed in which an electrostatic latent image formed by exposing a non-image portion of the charged photoreceptor 1 is developed with toner having a polarity opposite to the charged polarity of the photoreceptor 1. It is something that adopts. FIG. 2 is an explanatory diagram of normal development. On the other hand, FIG. 3 is an explanatory diagram of reversal development generally used in an image forming apparatus using a conventional laser writing apparatus.

  As shown in FIG. 2, in regular development, toner is adhered in the development process to non-exposed areas in the exposure process. That is, the development potential in normal development is the bias difference between the charging potential (= the potential of the non-exposed area) and the development bias. Here, the charging potential does not depend on whether the toner image exists or not, and can be maintained almost constant. In contrast, the problem that the development potential changes depending on the presence or absence of toner does not occur. Therefore, by applying regular development, it is possible to improve the problem that a difference occurs in the toner adhesion amounts for the second and subsequent colors.

  The pre-transfer charging device 5 is also the same scorotron charger as the charging device 2, and charges the toner image superimposed on the photoreceptor 1 to −400V.

  The transfer belt device 6 includes a transfer belt 61 and two rollers 62 and 63 that stretch the belt. Of the two rollers, a roller 62 disposed inside the transfer belt 61 in a region in contact with the circumferential surface of the photoreceptor 1 is a transfer roller for transferring the toner image of the photoreceptor 1 onto the recording paper 7 carried by the transfer belt 61. As a function. The roller 62 is a conductive elastic roller, and a transfer bias subjected to constant current control (+40 μA) is applied as a transfer bias. The recording paper 7 is conveyed by a conveying means from a paper bank (not shown), and conveyed to the transfer belt device 6 by the registration roller 10 in synchronization with the toner image formation on the photosensitive member 1. In the transfer belt device 6, the superimposed toner image on the photoreceptor 1 is transferred to a desired position on the recording paper 7 by the transfer bias applied to the roller 62.

  The fixing device 8 fixes the toner image on the recording paper 7 by heating and pressurizing the recording paper 7 onto which the toner image conveyed from the transfer belt device 6 is transferred, and discharges the recording paper 7 to the outside.

  The cleaning device 9 includes a cleaning blade, and removes toner remaining on the photoreceptor 1 without being transferred.

Next, each example in which a more characteristic configuration is added to the printer according to the embodiment will be described.
[Example 1]
The developing device 4 will be described in detail. In the developing device 4, the photoconductor 1 and the toner carrier 42 face each other in a non-contact manner so as not to disturb the toner image already formed on the photoconductor 1 when the color superimposing method on the photoconductor is performed. The non-contact development method is used.

  FIG. 4 is a schematic configuration diagram of the developing device 4 according to the first embodiment. The developing device 4 shown in FIG. 4 has a casing 41 in which toner can be carried on the surface in a non-stationary state, and a toner carrier 42 that is rotatably arranged, and a toner supply that supplies toner to the toner carrier 42 A toner supply roller 43 as a means, a toner storage portion 44 for storing toner, a toner supply device 45 for supplying toner in the toner storage portion 44 to the toner supply roller 43, and a toner on the toner carrier 42 And a toner regulating member 46 for regulating the layer thickness.

  The toner carrier 42 is disposed so as to face the photoconductor 1 in a non-contact manner, and carries the toner on the surface in a non-static state. The toner carrier 42 is rotated so as to have the same speed in the same direction (clockwise in FIG. 4) with respect to the photoreceptor 1 by a driving device (not shown). In the first exemplary embodiment, the toner carrier 42 has a cylindrical shape of 10 mm, is disposed with a distance (gap) of 0.20 mm between the toner carrier 42 and the photosensitive member 1, and is rotationally driven at a surface moving speed of 100 mm / sec. . Details of the configuration of the toner carrier 42 will be described later.

  The toner supply roller 43 is disposed in contact with the toner carrier 42 on the substantially opposite side of the development region, and supplies toner to the toner carrier 42 and charges the toner (provides charge). In the first exemplary embodiment, the toner supply roller 43 has a cylindrical shape of 10 mm, the amount of biting of the toner supply roller 43 with respect to the toner carrier 42 is set to 0.5 mm, and is rotated at a rotation number of 326 rpm by a driving unit (not shown). Further, the toner supply roller 43 and the toner carrier 42 are set to the same potential, and the toner is supplied from the toner supply roller 43 to the toner carrier 42.

  The toner carrier 42 develops the toner image by conveying the toner supplied from the toner supply roller 43 to the development region by the rotation of the toner carrier 42. During the conveyance to the development area, the toner regulating member 46 regulates the amount of toner adhered on the toner carrier 42 to be constant.

  When the toner on the toner supply roller 43 is consumed and low, the toner supply device 45 drives the toner supply device 45 to supply the toner stored in the toner storage unit 44 to the toner supply roller 43 side. To do.

  The toner used in the developing device 4 was a so-called polymerized toner produced by a polymerization method, and the toner manufactured to have a volume average particle diameter of 5.5 μm was used. The toner particle size was measured using a particle size measuring device “Coulter Counter TAII” manufactured by Coulter Electronics Co., Ltd., with an aperture diameter of 100 μm. Using substantially the same manufacturing method, toners of four colors of magenta (M), yellow (Y), cyan (C), and black (K) were produced. Further, the method for producing the toner is not limited to the above, and toner produced by a dispersion polymerization method or a pulverization method may be used.

In Example 1, with such a configuration of the developing device 4, a toner having an adhesion amount of 0.5 mg / cm ² is carried on the surface of the toner carrying member 42 and conveyed to the developing region, and the static image formed on the photoreceptor 1. Develop the electrostatic latent image.

  Next, the configuration of the toner carrier 42 will be described in detail. FIG. 5 is an enlarged view of the surface of the toner carrier 42. As shown in FIG. 5, the toner carrier 42 is one in which an electrode 421 is formed on a support substrate 422 and a surface protective layer 423 is further formed.

As the support substrate 422, a substrate made of an insulating material such as a glass substrate, a resin substrate, or a ceramic substrate, or a substrate made of a conductive material such as SUS, an insulating film such as SiO ₂ is formed, a polyimide film, or the like A substrate made of a flexible and deformable material can be used. In Example 1, a polyimide film having a thickness of 0.1 mm was used, and the support substrate 422 was formed by winding the polyimide film around an aluminum roller.

  The electrode 421 is formed by forming a conductive material such as Al or Ni—Cr on the support substrate 422 in a thickness of 0.1 to 10 μm, preferably 0.5 to 2.0 μm, and then using a photolithography technique or the like. It is formed by patterning into a required electrode shape. The width L (length in the direction of movement of the photoreceptor) of the plurality of electrodes 421 is desirably 1 to 20 times the volume average particle diameter of the toner. In Example 1, the electrode 421 was formed with a film thickness of 2 μm using Al as an electrode material. The width L, which is the pitch of the electrodes 421, was 50 μm. The electrode 421 is configured so that two electrically insulated (two-phase) electrodes are alternately arranged. These two systems of electrodes are hereinafter referred to as A phase and B phase and will be identified.

As the surface protective layer 423, for example, SiO ₂ , TiO ₂ , TiO ₄ , SiON, BN, TiN, Ta ₂ O _{5 and the} like are formed to a thickness of 0.5 to 10 μm, preferably 0.5 to 3 μm. Formed. In addition, inorganic nitride compounds such as SiN, Bn, and W can be used. In Example 1, it was formed with a film thickness of 3 μm using SiO ₂ .

  FIG. 6 is a waveform diagram of the drive voltage applied to the electrode 421 of the toner carrier 42. Va and Vb represent voltages applied to the A phase and the B phase of the electrodes, respectively. By applying such a driving voltage, the toner on the toner carrier 42 is carried in a non-stationary state. That is, as the drive voltage is switched, the toner always reciprocates while jumping between the electrodes. On the toner carrier 42, it is possible to realize a state where the toner is stably carried while reciprocating at the same position. In FIG. 5, the toner carrier 42 rotates at the same speed as the photosensitive member 1 in the direction of the arrow in the drawing, and the toner is conveyed to the developing region by the rotational movement of the toner carrier 42. .

Here, +400 V, which is a temporal average value of the drive voltage in FIG. 6, corresponds to a so-called developing bias. With this development bias, the electrostatic latent image is developed by moving the toner toward the photoreceptor 1 in the development region. In Example 1, with the configuration of the developing device 4 as described above, the contact condition of the toner regulating member 46 was adjusted so that the toner having an adhesion amount of 0.5 mg / cm ² was adhered on the toner carrier 42.

Here, the toner adhesion amount on the photosensitive member 1 after passing through the development region is 0.5 mg / cm ² in the solid image region. Since the moving speed of the photosensitive member 1 and the moving speed of the toner carrier 42 are the same, the amount of toner to be developed on the photosensitive member 1 is regulated by the amount of toner carried on the toner carrier 42. It can be said that That is, in the solid image area, all the toner carried on the toner carrying body 42 has moved to the photoconductor 1 side.

  In such a color superimposing method using regular development, an image in which a large amount of toner such as secondary colors and tertiary colors are deposited on the photoreceptor 1, and the toner adhesion amount in the secondary and tertiary colors. There is a risk of problems such as a small amount. A small amount of toner adhering in the secondary and tertiary colors means that the color reproduction range is narrow, and a vivid output image cannot be performed, leading to a decrease in value for the user. . In order to cope with this problem, it is necessary to secure a high developing ability by setting a large amount of monochromatic toner adhesion in the on-photosensitive color superposition method. On the other hand, in the color superimposing method on the photoreceptor, non-contact is required. However, non-contact tends to decrease the developing ability and reduce the toner adhesion amount. For this reason, in order to obtain a high developing ability, an extremely large developing potential is required as compared with the prior art. This leads to a problem that the charging potential of the photosensitive member 1 must be set higher than in the conventional case when regular development is used in the color superimposing method on the photosensitive member, which increases the cost of the power supply device and the photosensitive member. This causes problems such as a decrease in the life of the drum.

Here, since the toner can be carried in a non-stationary state on the toner carrier 42 of the first exemplary embodiment, the toner is carried with a small adhesive force between the toner and the toner carrier 42. It becomes possible. For this reason, development with a low development potential can be realized. Specifically, a sufficient adhesion amount such as a toner adhesion amount of 0.5 mg / cm ² on the photosensitive member can be ensured in spite of a low potential development bias of + 400V. As described above, by using the color superimposing method on the photosensitive member together with the toner carrier 42 that holds the toner in a non-stationary state, it is possible to realize development with a low developing potential, and thus, the charged potential is compared with the conventional one. Therefore, it is possible to effectively suppress a decrease in the adhesion amount of toner images formed in an overlapping manner.

  In FIG. 6, the developing bias (average value of driving voltage) value (here, +400 V) is described. However, as a characteristic part of the present invention, the developing bias can be changed and switched to another value to form an image. It is configured to perform. This switching of the developing bias will be described in detail later.

  Here, the operation of the writing device 3 that generates laser light applied to the photosensitive member 1 corresponding to the output image data will be described. As shown in FIG. 1, based on input image data, an image processing apparatus 11 described later performs image processing to create output image data. The video signal processing unit 12 receives image data for output, stores data for the number of light emitting points (LD: laser diodes) on the line memory, and matches the signal (so-called synchronization signal) synchronized with the rotation of the polygon mirror. Then, the data on the line memory corresponding to each pixel is delivered to a PWM control unit (not shown) at a predetermined timing (pixel clock). In this embodiment, the number of light emitting points is one for each color. In the PWM controller, this data is converted into a pulse width modulation (PWM) signal and delivered to the LD driver. In the LD driver, the LD element (LD array) is optically modulated and driven with a predetermined light amount corresponding to the pulse width modulation signal. In this manner, pulse width modulation (PWM) control is performed corresponding to the output image data of each color component, and laser light modulation driving is performed.

  The emitted light from the LD forms parallel light in the collimate lens and is cut into a light beam corresponding to a desired beam diameter by the aperture. The light beam after passing through the aperture passes through the cylindrical lens and enters the polygon mirror. The light beam reflected by the polygon mirror is condensed by a scanning lens (f-θ lens), and after being folded by a folding mirror, an image is formed on the surface of the photoreceptor 1 described above. In the printer of the present embodiment, optical writing by LD is performed at a resolution of 600 dpi. The PWM is manufactured to have 6 bits of freedom. However, in the image processing apparatus described later, the output image data is converted into 600 dpi 4 bit data after quantization in the pseudo halftone process, so that 4 bits in the PWM 6 bits are converted into the output image data (pseudo halftone). The light emission of the LD is controlled in association with the data after processing. For this reason, the LD emits light for 4 bits corresponding to the output image data (16 patterns including the non-lighted state).

 In this way, the light-modulated laser light forms an image on the photoconductor 1 and is scanned by the writing device 3 as described above, so that an electrostatic image corresponding to a desired image is formed on the photoconductor 1. A latent image can be formed. The process from developing this electrostatic latent image into a toner image to forming a toner image on the recording paper 7 is as described above. A full color image corresponding to the image data can be formed on the recording paper 7 in the order of operations described above.

  Next, the image processing apparatus 11 will be described in detail. FIG. 7 is a schematic configuration diagram of the image processing apparatus 11. The image processing apparatus 11 performs image processing on the input image data 100 and converts it to output data 110. The image processing apparatus 11 includes a color separation processing apparatus 102 including a color correction unit 103 and a BG / UCR unit 104, a memory 105, and a printer. γ correction means 106 and dither processing means 107 are provided. In FIG. 7, the digital image signal which is input image data 100 is an RGB 8-bit color image signal, and a color image is processed by the color correction unit 103 and the BG / UCR unit 104 of the color separation processing unit 102 of the image processing unit 11. Signals CMYK are converted into 8-bit color image signals. In this embodiment, conversion to CMYK data is performed by a method called DLUT (Direct Look up Table).

  In the DLUT, the input color space (RGB) is divided into small unit cubes, and output values (CMYK) corresponding to the respective grid points are determined by a method described later, and held in the DLUT format. The input values other than the grid points are calculated by a complementary operation. In this embodiment, tetrahedral complementation (Tetrahedral complementation) is used as the complement calculation method. In tetrahedron interpolation, a unit cube is divided into six unit tetrahedrons to perform a complement operation. By such a method, an 8-bit color image signal for each color of CMYK is obtained.

  Next, a method for creating the above-described DLUT will be described. In order to create a DLUT, it is first necessary to construct a color prediction model. The present inventors, for all combinations of CMYK 10 gradation steps, have monochromatic characteristic data and color mixing characteristics. Data was prepared. In other words, 5000 color patches are actually formed on paper using an on-photoreceptor color superposition experiment machine, and the Lab color is measured by an automatic colorimeter, and this color prediction model is constructed. used. The color prediction model is constructed by statistically processing the 5000 patch color measurement data prepared as described above using a multiple regression model. In this way, the above-described DLUP was created by calculating the value of each lattice point of the above-described DLUT using the constructed color prediction model.

  The signal separated into four colors by the color separation processing device 102 is temporarily stored in the memory 105. Then, the printer γ correction unit 106 and the dither processing unit 107 are applied to the image signal stored in the memory 105. The printer γ correction unit 106 performs conversion from CMYK data (8 bits) to CMYK data (8 bits) using a printer γ table which is a one-dimensional LUT (lookup table). By performing such γ correction, a predetermined input / output relationship (a reflection amount for detecting, in place of the toner adhesion amount or adhesion amount on the photoreceptor 1 with respect to CMYK data after color correction, which is set in advance) The relationship with the output value of the sensor). This is done to absorb and correct that the input / output relationship fluctuates due to fluctuation factors such as environmental fluctuations and fluctuations with time.

  In the dither processing unit 107 which is a pseudo halftone processing device, a matrix in which threshold data called a dither matrix is entered in the image processing device 11 in advance, and the CMYK data converted by the printer γ correction unit 106 is stored. The pseudo halftone processing is performed by comparing the CMYK data value with the threshold data described in the dither matrix for each pixel. In the present embodiment, the dither processing for converting from CMYK 8-bit data to CMYK 4-bit data is performed by this dither processing. As the dither processing means 107, any dither processing means known in the art can be applied to this embodiment.

  Next, it will be described that the developing bias can be changed, which is a feature of the present invention. As described above, the drive voltage applied to the electrode of the toner carrier 42 is the drive voltage shown in FIG. 6 (the voltage corresponding to the developing bias of +400 V). The second drive voltage different from that shown in FIG. 6 can be applied to the electrode of the toner carrier 42. Hereinafter, the drive voltage illustrated in FIG. 6 is referred to as a first drive voltage.

  FIG. 8 is a waveform diagram of the second drive voltage applied to the electrode 421 of the toner carrier 42. The waveform of the second drive voltage shown in FIG. 8 is obtained by reducing the waveform of the first drive voltage shown in FIG. 6 by 100V. For this reason, in FIG. 8, the value corresponding to the developing bias is +300 V, and the image can be output by switching the developing bias to this value.

  FIG. 9 is an explanatory diagram for switching and applying the developing bias to the developing device 4. In FIG. 9, voltages such as Va, Vb, and Vsup are applied from the drive circuit 424 to the A-phase electrode and the B-phase electrode, which are electrodes of the toner carrier 42, and the toner supply roller 43, respectively. The drive circuit 424 is configured to switch the voltages Va, Vb, and Vsup and apply them to the developing device 4 based on the switching instruction signal 13 for instructing voltage switching. For example, when the value of the switching instruction signal 13 is 0, an AC voltage of +250 V to +550 V as shown in FIG. 6 is applied to Va and Vb, and +400 V, which is the average value of this AC voltage, is applied to Vsup. To do. Hereinafter, this is referred to as a first developing bias. On the other hand, when the value of the switching instruction signal 13 is 1, an AC voltage of +150 V to +450 V as shown in FIG. 8 is applied to Va and Vb, and +300 V, which is an average value of this AC voltage, is applied to Vsup. To do. Hereinafter, this is referred to as a second developing bias. In this way, the average value of the AC voltage applied to Va and Vb is switched according to the value of the switching instruction signal 13. As described above, the average value of the AC voltage applied to Va and Vb corresponds to the developing bias, and the difference between the average value of the AC voltage and the post-exposure potential corresponds to the background potential.

  As described above, either development bias can be selected and set from the first or second development bias. For printers that perform regular development, if the difference between the average value of the applied AC voltage and the post-exposure potential is larger, unnecessary toner will not adhere to the background area, and background fog will not occur, but a highlight image will be produced. It has the characteristic that it is difficult. On the other hand, if the difference between the average value of the applied AC voltage and the post-exposure potential is smaller, highlight images are more likely to appear, but unnecessary toner tends to adhere to the background area, and background fog is likely to occur. It has characteristics such as. Therefore, in the printer having the above-described configuration, for example, for the purpose of preventing “color mixing with a high toner adhesion image in regular development”, the value of the switching instruction signal 13 is set to 0 so that the background potential can be increased. Select a bias. For the purpose of preventing “deterioration of highlight reproducibility in regular development”, the second development bias is selected with the value of the switching instruction signal 13 set to 1 so that the background potential can be reduced. More specifically, when outputting an image that emphasizes vivid appearance such as a POP image or a graphics image, the first development bias is selected, and when outputting a photograph (natural image). The second development bias can be selected. In the first embodiment, such development bias switching is performed for all the developing devices 4M, 4Y, 4C, and 4K of magenta (M), yellow (Y), cyan (C), and black (K).

  With this configuration, one printer outputs both an image that prevents "color mixing with a high toner adhesion image in regular development" and an image that "deteriorates highlight reproducibility in regular development". Is possible. Therefore, the problem of using both regular development and the problem of coexistence of “color mixing with a high toner adhesion image in regular development” and “deterioration of highlight reproducibility in regular development” is a substantial problem. The level can be reduced to a level that does not become a problem.

  In Example 1, the charging potential of the photosensitive member 1 remains fixed at +700 V even when the developing bias is switched. However, since the difference between the charging potential corresponding to the developing potential and the average value of the AC voltage is changed by switching the developing bias, the charging potential may be switched so that this does not change. Specifically, when the voltage for driving the developing device 4 is switched to the second drive voltage (FIG. 8), the charging potential is set to +600 V in accordance with this.

[Example 2]
Next, Example 2 will be described. The second embodiment has the same configuration as that of the first embodiment except that the second developing bias applied to the developing device 4 is different. FIG. 10 is an explanatory diagram showing another modified example of the drive voltage applied to the electrode 421 of the toner carrier 42. Also in this case, when the value of the switching instruction signal 13 is 0, the first developing bias shown in FIG. 6 is applied. On the other hand, when the value of the switching instruction signal 13 is 1, Va and Vb apply an AC voltage of +100 V to +700 V shown in FIG. 10 as the second developing bias, and an average of the AC voltage is applied to Vsup. A value of +400 V is applied. That is, in the printer of Example 2, the peak-to-peak voltage of the applied AC voltage differs between the first developing bias and the second developing bias. In a printer that performs regular development, the smaller the peak-to-peak voltage in the drive voltage applied to the toner carrier 42 is, the more difficult the background fog is to occur, but the highlight image has poor reproducibility. On the other hand, if the peak-to-peak voltage in the drive voltage applied to the toner carrier 42 is smaller, highlight images are more likely to appear, but unnecessary toner tends to adhere to the background area, and background fog is likely to occur. It comes to have the characteristic that it ends up. Therefore, in the second embodiment as well, for the purpose of preventing, for example, “color mixing with a high toner adhesion image in regular development”, the value of the switching instruction signal 13 is set to 0 so that the background potential can be increased. Select. For the purpose of preventing “deterioration of highlight reproducibility in regular development”, the second development bias is selected with the value of the switching instruction signal 13 set to 1 so that the background potential can be reduced. Also in the second embodiment, such development bias switching is performed for all the developing devices 4M, 4Y, 4C, and 4K of magenta (M), yellow (Y), cyan (C), and black (K).

[Example 3]
Next, Example 3 will be described. In the third embodiment, an output mode as a color reproduction condition changing unit that can select an output mode that is a color reproduction characteristic of an image to be output and changes an image forming condition relating to the color reproduction characteristic in response to the output mode selection result in the first embodiment. It has a switching device. FIG. 11 is an explanatory diagram of a control unit of a printer having the output mode switching device 15 according to the third embodiment. In the control unit of this printer, upon receiving the output mode selection result 16, the output mode switching device 15 switches the switching instruction signal corresponding to each color of magenta (M), yellow (Y), cyan (C), and black (K). 13M, 13Y, 13C, and 13K are output. The switching instruction signals 13M, 13Y, 13C, and 13K are connected to the driving circuits 424M, 424Y, 424C, and 424K corresponding to the colors M, Y, C, and K, and the driving circuits 424M, 424Y, 424C, and 424K are switched. The developing bias is switched according to the values of the instruction signals 13M, 13Y, 13C, and 13K.

  Development bias switching by the drive circuits 424M, 424Y, 424C, 424K is the same as in the first embodiment. In the third embodiment, the output mode selection result 16 that is the color reproduction characteristic is a result of selecting either the vividness priority output mode (referred to as output mode 0) or the gradation priority output mode (output mode 1). Has come to correspond. When the output mode 0 is selected, the output mode switching device 15 outputs 0 to the drive circuits 424M, 424Y, 424C, 424K as the values of the switching instruction signals 13M, 13Y, 13C, 13K. In this case, the voltage of the waveform shown in FIG. 6 is applied to the electrode of the toner carrier 42, and the first developing bias is selected. On the other hand, when the output mode 1 is selected, the output mode switching device 15 outputs 1 to the drive circuits 424M, Y, C, K as the values of the switching instruction signals 13M, 13Y, 13C, 13K. In this case, the voltage of the waveform shown in FIG. 8 is applied to the electrode of the toner carrier 42, and the second developing bias is selected. Here, the absolute value of the first developing bias is 400 V, the absolute value of the second developing bias is 300 V, and the relationship of the absolute value of the first developing bias> the absolute value of the second developing bias is satisfied. Further, as described above, the first development bias corresponds to the case where the output mode with priority on vividness is selected, and the second development bias corresponds to the priority on gradation. The output mode is selected.

[Example 4]
Next, Example 4 will be described. The fourth embodiment is a device for switching the developing bias corresponding to the selected output mode as in the third embodiment, and the color of the color separation processing device 102 of the image processing device 11 corresponding to the selected output mode. The color separation method is also switched.

  FIG. 12 is an explanatory diagram of a control unit of a printer having the output mode switching device 15 according to the fourth embodiment. As shown in FIG. 12, in the control unit of this printer, upon receiving the output mode selection result 16, the output mode switching device 15 outputs switching instruction signals 13M, 13Y, 13C, and 13K corresponding to each color of CMYK. The switching instruction signal 13P is also output to the image processing apparatus 11. Similarly to the third embodiment, the switching instruction signals 13M, 13Y, 13C, and 13K are connected to the drive circuits 424M, 424Y, 424C, and 424K corresponding to the colors CMYK, and the switching instruction signals 13M, 13Y, 13C, and 13K are connected. The developing bias is switched according to the value of. The development bias switching in the drive circuits 424M, 424Y, 424C, and 424K is the same as that in the third embodiment. In the fourth embodiment, unlike the third embodiment, the color separation processing device 102 in the image processing device 11 switches the color separation method in response to the switching instruction signal 13P from the output mode switching device 15.

  FIG. 13 is a schematic configuration diagram of the image processing apparatus 11 according to the fourth embodiment. In FIG. 13, in addition to the input image data 100, the switching instruction signal 13P is input to the color separation processing apparatus 102 of the image processing apparatus 11. The color correction means 103 constituting the color separation processing device 102 converts the RGB format image data, which is the input image image data 100, into CMY format image data. At this time, as described above, the DLUT method is used. Conversion is in progress. In the fourth embodiment, according to the value of the switching instruction signal 13P, the DLUT data 101 referred to at the time of conversion is switched to create CMYK format image data. The DLUP data 101 stores data in two DLUT formats, data 0 and data 1, in advance, which data is used is determined by the value of the switching instruction signal 13P.

  In the fourth embodiment, when the value of the switching instruction signal 13P is 0 (corresponding to a large developing bias), the CMYK data is assigned so that the outermost portion of the color reproduction range (color gamut) of the image forming apparatus is used. DLUT data (data 0) is applied. Further, when the value of the switching instruction signal 13P is 1 (corresponding to a small development bias), the outermost outline of the color reproduction range (color gamut) of the image forming device is not used up (gradation and smoothness). The DLUT data (data 1) for allocating CMYK data is used so that the inner area is used (so that a color change can be realized). It's not easy to tell if the color reproduction range has been used up or down, but the size of the color reproduction range being used is relatively easy to understand. From the output print sample (when colorimetry is performed), it is easily determined whether DLUP data is switched to create CMYK data or not.

[Example 5]
Next, Example 5 will be described. The fifth embodiment is a printer of the fourth embodiment, in which an output mode instruction device 17 for instructing the output mode selection result 16 to the output mode selection device 15 is provided.
FIG. 14 is an explanatory diagram of a control unit of a printer having the output mode instruction device 17 according to the fifth embodiment. In FIG. 14, the user using the printer can instruct the output mode using the output mode instruction device 17. As the output mode instruction device 17, an instruction screen of software (printer driver) displayed on a personal computer can be used. As a matter of course, the output mode instruction device 17 may be of another type. For example, a button or an instruction screen attached to the main body of the printer may be used.

[Example 6]
Next, Example 6 will be described. In the sixth embodiment, the printer of the fourth embodiment is provided with an input image data discriminating device 18 for outputting the output mode selection result 16 to the output mode selecting device 15 based on the input image data 100.
FIG. 15 is an explanatory diagram of a control unit of a printer having the input image data discrimination device 18 according to the sixth embodiment. In FIG. 15, the input image data discriminating device 18 to which the input image data 100 is inputted discriminates the type of the input image data 100 and outputs the discrimination result as the output mode selection result 16 to the output mode switching device 15. . On the other hand, the input image data 100 is input to the image processing device 11 after the input image data determination device 18 performs the above determination. The input image data discriminating device 18 discriminates the image type (whether it is a graphics-type image or a photographic-type image) from the object attribute of the input image data 100 or the like. In addition to this, the input image data discriminating apparatus 18 may discriminate in terms of whether there are many (or not) vivid colors used in the image. . Furthermore, the discrimination method in the input image data discrimination device 18 can be combined with any known technique, and the sixth embodiment can be configured.

[Example 7]
Next, Example 7 will be described. The seventh embodiment is different from the first embodiment in the toner carrier 42 of the developing device 4. FIG. 16 is a schematic configuration diagram of a developing device according to the seventh embodiment. In the developing device 4 of Example 7, the construction and operation of the developing devices 4Y, 4M, 4C, and 4K for magenta, yellow, cyan, and black are the same, so the subscripts Y, M, C, and K are changed. I will omit the explanation. The developing device 4 in FIG. 16 supplies a toner to a toner carrier 42 in the form of a roller that can carry the toner in a casing 41 by a conveying electric field formed on the surface and convey the toner to the developing region. A toner supply roller 43 that performs toner supply, a toner storage portion 44 that stores toner, a toner supply device 45 that supplies toner in the toner storage portion 44 to the toner supply roller 43, and a toner layer thickness on the toner supply roller 43 And a toner regulating member 47 that regulates the above.

  The toner carrying member 42 is disposed so as to face the photoconductor 1 in a non-contact manner, and carries the toner on the surface thereof in a non-stationary state. In Example 7, the toner carrier 42 has a cylindrical shape of 10 mm, and the distance (gap) between the toner carrier 42 and the photosensitive member 1 is 0.20 mm, and the toner carrier 42 is disposed in a stationary state. Since the details of the configuration of the toner carrier 42 will be described later, the description thereof is omitted here.

  The toner supply roller 43 is disposed so as to face the toner carrying member 42 in a non-contact manner on the substantially opposite side of the developing region, and supplies toner to the toner carrying member 42. In Embodiment 7, the toner supply roller 43 has a cylindrical shape of 12 mm, the distance (gap) between the toner supply roller 43 and the toner carrier 42 is set to 0.20 mm, and the rotational speed is 326 rpm by a driving unit (not shown). It is rotating. Further, by providing a potential difference of 1.3 kV between the toner supply roller 43 and the toner carrier 42, the toner is supplied from the toner supply roller 43 to the toner carrier 42.

  The toner restricting member 47 is disposed to face the toner supply roller 43 and restricts the amount of toner adhering to the toner supply roller 43 to be constant, and toner is supplied to the toner supply roller 43 and the toner restricting member 47 at this portion. By being rubbed with each other, a predetermined charge amount is obtained.

  When the toner on the toner supply roller 43 is consumed and decreased, the toner replenishing device 45 drives the replenishing device to replenish the toner stored in the toner storage unit 44 to the supply roller 43 side.

  The toner used in the developing device 4 is the same as that used in the first embodiment.

In Example 7, such a configuration of the developing device 4 enabled the toner amount of 0.7 mg / cm ² to be carried on the surface of the toner carrier 42. The toner carrying member 42 conveys the carried toner to the developing area and develops the electrostatic latent image formed on the photoreceptor 1.

  Next, the configuration of the toner carrier 42 of Example 7 will be described in detail. FIG. 17 is an enlarged view of the surface of the toner carrier 42 of the seventh embodiment. As shown in FIG. 17, the toner carrier 42 of Example 7 has a plurality of electric fields for generating, generating, and collecting the toner T, which is powder, on the support substrate 422. The electrode 421 is formed, and the surface protective layer 423 is further formed and integrated. Different drive waveforms Va, Vb, and Vc of n phases (here, three phases) for generating a required electric field are applied from the drive circuit 424 to each electrode 421 of the toner carrier 42. The toner T is transferred to the vicinity of the photosensitive member 1 by the traveling wave electric field formed between the electrodes 421 to which the driving waveforms Va, Vb, and Vc are applied, and the toner T is attached to the latent image of the photosensitive member 1 to form the toner. An image is formed, and the toner T that has not been used in the development is collected on the toner carrier 42 side. In addition, for each electrode 421 of the toner carrier 42, in the development region, the toner T is directed toward the photosensitive member 1 with respect to the image portion of the latent image on the photosensitive member 1, and with respect to the non-image portion. The toner T forms an electric field in a direction toward the opposite side (toner carrier side) from the photosensitive member 1, and the toner T is attached to the latent image for development. As a result, in the development area, the toner adheres to the latent image on the photoconductor 1 to be visualized, and the toner that has not contributed to the development is collected downstream in the rotation direction (movement direction) of the photoconductor 1.

As the support substrate 422 of the toner carrier 42 in FIG. 17, an insulating film such as SiO ₂ is formed on a substrate made of an insulating material such as a glass substrate, a resin substrate or a ceramic substrate, or a substrate made of a conductive material such as SUS. A substrate made of a material that can be deformed flexibly, such as a film formed or a polyimide film, can be used. In Example 7, a polyimide film having a thickness of 0.1 mm was used.

  The electrode 421 is formed by forming a conductive material such as Al or Ni—Cr on the support substrate 422 in a thickness of 0.1 to 10 μm, preferably 0.5 to 2.0 μm, and then using a photolithography technique or the like. It is formed by patterning into an electrode shape. The width L of the plurality of electrodes 421 in the powder traveling direction is set to be 1 to 20 times the average particle diameter of the powder to be moved, and the distance R of the electrodes 421 in the powder traveling direction is also moved. It is 1 to 20 times the particle size. In Example 7, the electrode 421 was formed with a film thickness of 2 μm using Al as an electrode material. The width L, which is the pitch of the electrodes 421, was 50 μm.

As the surface protective layer 423, for example, SiO ₂ , TiO ₂ , TiO ₄ , SiON, BN, TiN, Ta ₂ O _{5 and the} like are formed to a thickness of 0.5 to 10 μm, preferably 0.5 to 3 μm. Formed. In addition, inorganic nitride compounds such as SiN, Bn, and W can be used. In Example 7, it was formed with a film thickness of 3 μm using SiO ₂ .

  Next, the principle of electrostatic conveyance of toner in the toner carrier 42 configured as described above will be described. By applying an n-phase (three-phase in Example 7) driving waveform to the plurality of electrodes 421 of the toner carrier 42, a phase-shift electric field (traveling wave electric field) is generated by the plurality of electrodes 421, thereby conveying the substrate. The charged toner on 422 receives repulsive force and / or suction force and moves in the transfer direction including hopping and conveyance.

  For example, with respect to the plurality of electrodes 421 of the toner carrier 42, as shown in FIG. 18, a three-phase pulse-shaped drive waveform (drive signal) A (change between a ground G (0V) and a negative voltage − is provided. A phase), B (B phase), and C (C phase) are applied at different timings. At this time, as shown in FIG. 19, the negatively charged toner T is present on the toner carrier 42, and a plurality of continuous electrodes 421 on the toner carrier 42 are respectively “−” and “−” as indicated by 1 in FIG. ”,“ G ”,“ − ”, and“ − ”are applied, the negatively charged toner T is positioned on the“ G ”electrode 421 (center electrode). At the next timing, “G”, “−”, “G”, “G”, and “−” are respectively applied to the plurality of electrodes 421 as shown in FIG. Since a repulsive force acts between the “-” electrode 421 and an attractive force (mirror force) acts between the “G” electrode 421 and the negatively charged toner T, the negatively charged toner T acts on the right “G” electrode. Move to the 421 side. Further, at the next timing, “G”, “−”, “−”, “G”, and “−” are respectively applied to the plurality of electrodes 421 as indicated by 3, and the negatively charged toner T is shifted to the right by one. The “G” moves to the electrode 421 side. In this way, by applying a multi-phase driving waveform whose voltage changes to the plurality of electrodes 421, a traveling wave electric field is generated on the transport substrate 421, and the negatively charged toner T is transported in the traveling direction of the traveling wave electric field. And move while hopping. In the case of positively charged toner, the drive waveform changes in the same direction by reversing the drive waveform change pattern.

  Next, the configuration of the drive circuit 424 will be described. FIG. 20 is a schematic configuration diagram of the drive circuit 424. The drive circuit 424 generates a pulse signal from a pulse signal generation circuit 425, and receives pulse signals from the pulse signal generation circuit 425 to generate and output drive waveforms Va, Vb, and Vc. 426c.

  The pulse signal generation circuit 425 receives, for example, a logic level input pulse and is a set (one set of three) of pulses that are phase-shifted to 120 °, and is included in the waveform amplifiers 426a, 426b, and 426c in the next stage. Means, for example, a transistor is driven to generate and output a pulse signal having an output voltage of 10 to 15 V at a level capable of switching from 100 to 600 V.

  In the developing device 4, a driving voltage as shown in FIG. 21 is applied to the three-phase electrodes of the toner carrier 42. This waveform is a voltage waveform obtained by superimposing a +400 V DC component on an AC component having a peak-to-peak voltage of 300 V and a so-called duty ratio of 50%. In the seventh embodiment, driving is performed at a frequency of 667 Hz. The development bias that triggers development of the latent image with toner in the development region is considered to be the time average value of the drive voltage described above. That is, in the developing device 4 of Example 7, the developing bias is + 400V.

  By applying a drive voltage having such a waveform to the toner carrier 42, the toner can be transported to the development area by the toner carrier 42, and the toner is also adhered to the image area in the development area. Can do.

In the developing device 4, the toner on the toner carrying member 42 is conveyed to the developing region by the drive voltage applied to the electrode 421, so that it is carried in a non-stationary state. In the developing device 4, as already described, the toner is carried on the toner carrier 42 with an adhesion amount of 0.7 mg / cm ² . In the developing area, as described above, +400 V is applied as a developing bias to the toner carrier 42, and thus toner adheres to the image area. At this time, the toner adhesion amount on the photoreceptor 1 in the image region was 0.7 mg / cm ² .

The toner transported on the toner carrier 42 has a moving speed of 100 mm / sec because the electrode pitch of the toner carrier is 150 μm (because it is a three-layer electrode with a 50 μm pitch) and the drive voltage frequency is 667 kHz. Since the toner amount on the toner carrier 42 is 0.7 mg / cm ² , the toner conveyance amount on the toner carrier 42 is 7 mg / (cm · sec). On the other hand, the toner adhesion amount on the photosensitive member 1 after passing through the development region is 0.7 mg / cm ² as described above, and the linear velocity of the photosensitive member 1 is 100 mm / sec. That is, all the toner carried on 42 has moved to the photosensitive member 1 side. That is, in the configuration of the seventh embodiment, a state is realized in which the adhesion amount of the toner developed on the photosensitive member 1 is regulated by the toner amount carried on the toner carrier 42.

As described above, in the developing device 4 of Example 7, non-contact development is used so as not to disturb the toner image already formed on the photosensitive member 1 when performing color superposition on the photosensitive member 1. By using the toner carrier 42, it is possible to carry the toner with a low adhesion force between the toner and the toner carrier 42, and to realize development with a low development potential. Specifically, a sufficient adhesion amount such as 0.7 mg / cm ² of toner adhesion on the photosensitive member can be ensured in spite of a low potential development bias of + 400V.

  Furthermore, in Example 7, since the toner carrier 42 is stationary, the developing device 4 has few parts to be driven. When there are many drive parts, the parts are rubbed and toner leakage is likely to occur from the rubbed part. In the developing device 4 according to the seventh embodiment, since there are few driving parts, problems such as contamination inside the apparatus and adhesion to an image hardly occur due to toner leakage. Further, since the toner carrier 42 is not driven, there is an advantage that the distance between the photosensitive member 1 and the toner carrier 42 can be easily maintained, and the degree of freedom in mechanical design is great.

  Further, in the seventh embodiment, as in the first embodiment, the developing bias is switched. Specifically, in addition to the development bias corresponding to the first development bias +400 V described above, the development bias corresponding to the second development bias +300 V (DC component is +300 V and the AC component has the same waveform as FIG. 19). ) Can be applied, and the two developing biases can be switched.

[Example 8]
Next, Example 8 will be described. In the eighth embodiment, the toner carrier 42 of the developing device 4 of the seventh embodiment is configured to be rotatable. As in the seventh embodiment, by applying a multiphase voltage to the plurality of electrodes 421 arranged at predetermined intervals of the toner carrier 42, the toner is non-stationary by a traveling wave electric field formed between the plurality of electrodes. While being held in a state, it is conveyed to a region facing the photoreceptor 1. Further, the toner carrier 42 is configured to be rotated and moved by a driving device (not shown). In this printer, the toner carrier 42 is stationary during the image forming operation, and performs exactly the same operation as in the seventh embodiment. Further, the toner carrier is rotated during non-image formation. In Example 8, the peripheral speed of the toner carrier 42 rotates at 50 mm / sec.

  Thus, since the toner carrier 42 is configured to be movable on the surface, it is possible to cope with changing the portion of the toner carrier 42 facing the photosensitive member 1. That is, even if an abnormality occurs in the portion facing the photoconductor 1, the normal portion can be made to face the photoconductor 1 by moving this portion. For this reason, it is not necessary to replace the toner carrier 42 frequently, and the life of the toner carrier 42 can be extended.

[Example 9]
Next, Example 9 will be described. In the ninth embodiment, as in the eighth embodiment, the toner carrier 42 of the developing device 4 of the seventh embodiment is configured to be rotatable. However, in Embodiment 9, the toner carrier 42 is rotated even during the image forming operation. By applying a multiphase voltage to the plurality of electrodes 421 arranged at predetermined intervals of the toner carrier 42, the traveling wave electric field formed between the plurality of electrodes and the surface movement of the toner carrier 42, The toner is conveyed in a non-stationary state to a region facing the photoreceptor 1. Here, since the configuration of the electrodes and the frequency of the drive voltage are the same as in Example 7, the toner moving speed by the traveling wave electric field is 100 mm / sec as in Example 7. Further, since the toner carrier 42 is rotated at a peripheral speed of 50 mm / sec, the moving speed of the toner in the developing area is 150 mm / sec. As described above, by increasing the moving speed of the toner in the developing region, the toner adhesion amount on the toner carrier 42 can be made smaller than that in the seventh embodiment. In Example 9, the voltage applied to the toner supply roller 43 was adjusted so that the toner adhesion amount on the toner carrier 42 was 0.47 mg / cm ² . Specifically, the toner adhesion amount was obtained by setting the potential difference between the toner supply roller 43 and the toner carrier 42 to 1.2 kV.

  As described above, the toner is conveyed by the traveling wave electric field formed by applying the driving voltage to the toner carrier 42 and the toner carrier 42 itself is rotated, so that the amount of toner carried on the toner carrier 42 is small. However, more toner can be transported to the development area. When the toner carrying amount on the toner carrying member 42 is small, it is difficult to be adversely affected by a change in the carrying amount due to changes in temperature and humidity, so that highly stable toner carrying can be realized.

  In the above-described embodiment, one charging device 2M, 2Y, 2C, and 2K is provided for each color, that is, four charging devices are provided, and a printer capable of generating a full-color image on the photosensitive member 1 in one pass is provided. Used to describe the invention. However, this is not an essential item of the present invention, and is also applied to an apparatus that forms a full-color image by rotating the photoreceptor 1 a plurality of times, and the same effect can be obtained. For example, in an image forming apparatus that forms a full-color image in four passes using four color toners, a developing device 4 is provided for each color, but only one charging device 2 is provided on a single photoconductor 1. The charging device 2 may be configured to be used in common for each color. By sharing one charging device 2 for each color in this way, the number of charging devices 2 provided in the apparatus main body can be reduced, so that the apparatus main body can be further reduced in size and cost.

  In the above-described embodiment, the present invention is implemented using a developing device in which the toner carrier 42 is disposed in a non-contact manner with respect to the photoreceptor 1 and the toner is carried on the toner carrier 42 in a non-static state for development. explained. However, this is not an essential item of the present invention, and the present invention can be applied to a developing device such as non-contact one-component development and non-contact two-component development, and the same effect can be obtained.

As described above, according to the present embodiment, in the printer that sequentially forms a plurality of color toner images on the photosensitive member 1 as an image carrier and obtains a superimposed color image, the developing device 4 is a normal developing unit. The developing bias of the developing means can be changed. As a result, it is possible to cope with both “color mixing with a high toner adhesion image in regular development” and “deterioration of highlight reproducibility in regular development”. For example, if a high toner adhesion image has already been formed on the photoconductor and the post-exposure potential rises during the formation of latent images for the second and subsequent colors, prevention of “color mixing with a high toner adhesion image in regular development” For this purpose, the development bias is changed so that the background potential, which is the difference between the post-exposure potential and the development bias, can be increased. On the other hand, for the purpose of preventing "deterioration of highlight reproducibility in regular development", the background potential is reduced, but the development bias is changed so that the development potential, which is the difference between the charging potential and the development bias, can be increased. To do. In this way, by making the development bias changeable, in one image forming apparatus, an image in which “color mixing with a high toner adhesion image in normal development” and “deterioration of highlight reproducibility in normal development” are achieved. A printer capable of outputting both of the images that prevent the occurrence of the problem is realized.
Further, the printer has an output mode switching device 15 as color reproduction condition changing means for changing the image forming condition relating to the color reproduction characteristics in response to the output mode selection result which is the color reproduction characteristic of the output image. In the control unit of this printer, upon receiving the output mode selection result 16, the output mode switching device 15 switches the developing bias. Here, the output mode, which is the color reproduction characteristic of the output image, depends on what kind of image the user wants to output depending on the user's preference and the type of image to be output. For example, when the vivid appearance is important, it is desirable to output the image with the highest priority on preventing "color mixing with a high toner adhesion image in regular development", and the reproducibility and gradation of the highlight portion are desirable. In the case where importance is attached, it is desirable to output an image with the highest priority on preventing “deterioration of highlight reproducibility in regular development”. In this way, what the user gives priority to image output, that is, the development bias is appropriately changed according to the output mode selection result, but the user needs to directly instruct the operation itself such as switching the development bias. However, by specifying the items such as what points the user places importance on when outputting images and what kind of image to output, the appropriate development bias can be indirectly specified. Can be selected by switching. For this reason, the user does not need to be aware of the point of switching the developing bias, and can realize a printer that is easy to use.
Further, as the development bias that can be changed, two types satisfying the relationship of the absolute value of the first development bias> the absolute value of the second development bias can be selected. The output mode selection result 16 that is the color reproduction characteristic corresponds to the result of selecting either the vividness priority output mode or the gradation priority output mode. When the vividness priority output mode is selected, the first developing bias is selected by the output mode switching device 15. On the other hand, when the tone priority output mode is selected, the second developing bias is selected by the output mode switching device 15. In this way, it is not necessary to directly instruct the switching of the developing bias, and since the developing bias is switched and selected based on the output mode instructed indirectly by the user, the user is directly aware of items such as the switching of the developing bias. There is no need to do so, and a printer with good specifications can be realized. In addition, when the vividness priority output mode is selected, the above development bias value is set. As a result, the background potential increases, and the subsequent toner adheres to the portion where the toner image is formed on the photoreceptor. The problem of ending up is reduced. For this reason, vivid colors such as primary colors and secondary colors can be output while being vivid. On the other hand, when the tone priority mode is selected, the above development bias value is set. As a result, the background potential is reduced and the highlight area is reproduced well. For this reason, it becomes possible to output an image having a good gradation property, such as density change, color change and smoothness.
Further, in the color separation processing apparatus 102 that performs color separation of the input image data 100 into each color image data, two or more color separation methods are applied corresponding to the development bias setting conditions. For this reason, color separation data can be created according to each of the two image output characteristics by the color superimposing method on the photosensitive member, and the image formation conditions and the characteristics of the image data are matched to output a higher quality image. Can be performed.
Further, the two color separation methods of the color separation processing apparatus 102 are respectively a vividness-priority color separation method and a gradation-priority color separation method. Since these two color separation methods are switched corresponding to the two development bias values, the image data corresponding to the toner color is linked with the switching of the color reproduction characteristics by switching the development bias. Also switch for each color reproduction characteristic. The vivid color-priority color separation method is a color separation method in which color image data is created using the color reproduction range (color gamut) of the image forming apparatus as much as possible. On the other hand, the tone-priority color separation method is a color separation method in which color image data is created using the inside without greatly using the color reproduction range (color gamut) of the image forming apparatus. The reason why the color reproduction range is not greatly used is that the color reproduction range of the image forming device is an irregular shape, and if this irregular shape is used up to the outermost contour, color continuity and smooth gradation change will be caused. This is because it cannot be realized. (Because color steps, gradation inversion, etc. occur) For this reason, it is possible to output the image by matching the characteristics of the image forming device with the characteristics of the image data.
The output mode is selected according to the user's instruction. In terms of how to set the output mode when performing image output, the output mode preferred by most users can be determined to some extent depending on the image type, but it is different from many people Some users prefer the output mode, and there are aspects such as the user's preference being large. Therefore, the output mode can be selected according to the user's instruction, and the image quality according to the user's preference can be obtained.
Further, the selection of the output mode is determined from the input data 100 of the output image. When performing image output, how to set the output mode largely depends on the type of image to be output. More specifically, since bright colors are often used in POP images and graphics images, an output mode capable of vivid color reproduction is required. In addition, in a photograph, since the gradation property determines the superiority or inferiority of the image rather than the vividness, an output mode with excellent gradation property is required. Therefore, an image type is determined from the input image data, and an appropriate development bias is selected. As a result, the selection of an appropriate development bias depending on the image type is completely automated, and the user does not have any troublesome work. That is, it is possible to obtain a high-quality image by appropriately switching the developing bias without burdening the user with troublesome work.
In addition, the color superimposing method on the photoconductor is employed together with the toner carrier 42 that can carry the toner in a non-stationary state. Since the toner carrier 42 can be carried while reducing the adhesion force between the toner and the toner carrier 42, even with non-contact development with low development capability, development with a low development potential can be realized. Can do. In other words, it is possible to effectively suppress a decrease in the adhesion amount of the toner images formed in an overlapping manner despite the low potential developing bias. Therefore, it is possible to solve the problem that the target color cannot be reproduced due to the decrease in the adhesion amount of the toner image formed in an overlapping manner and the problem of the decrease in the color reproduction range, and a high-quality image is obtained. be able to.
Further, as the toner carrier 42, a traveling wave electric field formed between a plurality of electrodes by applying a multiphase voltage to the plurality of electrodes 421 arranged side by side at a predetermined interval is used. In some cases, the toner is hopped on the toner carrier while the toner is conveyed to the opposite area. As a result, the toner can be held on the toner carrier 42 in a non-static state. Since the toner carrier 42 is used without being driven, it is possible to realize a printer in which troubles such as contamination inside the apparatus and adhesion to an image hardly occur due to toner leakage. In addition, since the toner carrier 42 is not driven, there is an advantage that the distance between the photosensitive member 1 and the toner carrier 42 can be easily maintained, and the degree of freedom in designing is large in performing mechanical design.
Further, the toner carrier 42 itself may be moved on the surface by conveying the toner to a region facing the photoreceptor 1 using the traveling wave electric field. The developing device 4 is configured to transport toner while being carried by a traveling wave electric field formed between a plurality of electrodes 421, and to remove the toner on the toner carrier as the surface of the toner carrier 42 itself moves. It is conveyed to a region facing the photoreceptor 1. Here, the toner carrier 42 is stationary when the image is formed, and the surface moves when the image is not formed. For example, even if an abnormality occurs in the portion facing the photosensitive member 1, this portion The normal portion can be made to face the photosensitive member 1 by moving the toner, and it is not necessary to frequently replace the toner carrier 42.
Further, in the case of moving the surface of the toner carrier 42 during image formation, the toner carrier 42 can be transported by moving the surface of the toner carrier 42 itself in addition to the toner transport by the traveling wave electric field. By adding transport by movement of the surface of the toner carrier 42 itself, more toner can be transported to the development area even if the amount of toner carried on the toner carrier 42 is small. As the toner carrying amount on the toner carrying body 42 is small, it is difficult to be adversely affected by the change in the carrying amount due to changes in temperature and humidity, so that highly stable toner carrying can be realized.
Further, as a toner carrier, a toner carrier is formed by using a oscillating electric field formed between a plurality of electrodes by applying a multiphase voltage to a plurality of electrodes 221 arranged side by side at a predetermined interval. The toner is held in a non-static state on 42. Further, the toner on the toner carrier 42 is transported to a region facing the photoreceptor 1 by the surface movement of the toner carrier 42. In the developing device 4, the reciprocating motion is repeated at the same position without transferring the toner by the oscillating electric field formed between the plurality of electrodes. However, on average (time average), it remains at the same position on the toner carrier. The toner is transferred to the development area by moving the surface of the toner carrier 42. As described above, since the toner is not transported by the electric field, there is a problem that the toner is trapped by the foreign matter and cannot be successfully transported to the downstream portion due to a trouble such as a foreign matter adhering to the toner carrier 42. Does not occur. That is, it is possible to provide a developing device that is tough against foreign matter adhering to the toner carrier 42. Further, by using such a toner carrier, a relatively wide range of toner amounts can be held on the surface of the toner carrier, and there is an advantage that the degree of freedom is large.
In addition, when used in a color image forming apparatus having a four-color developing device, C (cyan), M (magenta), Y (yellow), K (black), and a high-quality full-color image can be obtained. Become.

1 is a schematic configuration diagram of a main part of a printer according to an embodiment. Explanatory drawing of the regular development employ | adopted as the printer which concerns on this embodiment. Explanatory drawing of the reversal development employ | adopted with the conventional printer. 1 is a schematic configuration diagram of a developing device according to Embodiment 1. FIG. FIG. 3 is an enlarged view of the surface of the toner carrier of Example 1. FIG. 4 is a waveform diagram of a first drive voltage applied to an electrode of a toner carrier of Example 1. 1 is a schematic configuration diagram of an image processing apparatus according to Embodiment 1. FIG. FIG. 6 is a waveform diagram of a second drive voltage applied to the electrode of the toner carrier of Example 1. FIG. 3 is an explanatory diagram of switching and applying a developing bias to the developing device of Embodiment 1. FIG. 6 is a waveform diagram of a second drive voltage applied to an electrode of a toner carrier of Example 2. FIG. 6 is an explanatory diagram of a control unit of a printer having an output mode switching device according to a third embodiment. FIG. 9 is an explanatory diagram of a control unit of a printer having an output mode switching device according to a fourth embodiment. FIG. 6 is a schematic configuration diagram of an image processing apparatus according to a fourth embodiment. FIG. 10 is an explanatory diagram of a control unit of a printer having an output mode instruction device according to a fifth embodiment. FIG. 10 is an explanatory diagram of a control unit of a printer having an input image data determination device according to a sixth embodiment. FIG. 10 is a schematic configuration diagram of a developing device according to Embodiment 7. FIG. 9 is an enlarged view of the surface of a toner carrier of Example 7. FIG. 10 is a model diagram of a waveform of a drive voltage applied to an electrode of a toner carrier of Example 7. FIG. 10 is a model diagram of toner conveyance by driving voltage in the seventh embodiment. FIG. 10 is a schematic configuration diagram of a drive circuit according to a seventh embodiment. FIG. 10 is a waveform diagram of a drive voltage applied to an electrode of Example 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device 3 Writing device 4 Developing device 5 Pre-transfer charging device 6 Transfer belt device 7 Recording paper 8 Fixing device 9 Cleaning device 11 Image processing device 12 Video signal processing unit 13 Switching instruction signal 15 Output mode switching device 16 Output Mode selection result 17 Output mode indicating device 18 Input image data discriminating device 41 Developing casing 42 Toner carrier 43 Toner supply roller 44 Toner container 45 Toner replenishing device 46 Toner regulating member (on toner carrier)
47 Toner regulating member (on toner supply roller)
DESCRIPTION OF SYMBOLS 100 Input image data 101 DLUT data 102 Color separation processing apparatus 103 Color correction means 104 BG / UCR means 105 Memory 106 Printer gamma correction means 107 Dither processing means 110 Output image data 421 Electrode 422 Support substrate 423 Surface protection layer 424 Drive circuit 425 pulse Signal generation circuit 426a, b, c Waveform amplifier

Claims (12)

An image carrier;
Charging means for charging the image carrier;
Latent image forming means for exposing the image carrier charged by the charging means to form a latent image for each color;
A plurality of developing means for visualizing the latent images formed on the image carrier with different color toners,
For each color, charging by the charging unit, forming a latent image by the latent image forming unit, and developing by the developing unit are performed to sequentially form toner images of the respective colors on the image carrier and form a superimposed color image. In the obtained image forming apparatus,
At least one developing unit that forms a toner image on an image carrier on which a toner image has already been formed among the plurality of developing units is configured to use a toner having a polarity opposite to the charged polarity of the image carrier, An image forming apparatus comprising: a normal developing unit that develops an exposure unit, and the development bias of the normal developing unit can be changed. An image carrier;
Charging means for charging the image carrier;
Latent image forming means for exposing the image carrier charged by the charging means to form a latent image for each color;
A plurality of developing means for visualizing the latent images formed on the image carrier with different color toners,
For each color, charging by the charging unit, forming a latent image by the latent image forming unit, and developing by the developing unit are performed to sequentially form toner images of the respective colors on the image carrier and form a superimposed color image. To get
An image forming apparatus comprising color reproduction characteristic selecting means for selecting a color reproduction characteristic of the color image, and color reproduction condition changing means for changing an image forming condition relating to the color reproduction characteristic based on a selection result of the color reproduction characteristic selecting means In
At least one developing unit that forms a toner image on an image carrier on which a toner image has already been formed among the plurality of developing units is configured to use a toner having a polarity opposite to the charged polarity of the image carrier, An image forming apparatus comprising: a normal developing unit that develops an exposure unit, wherein the color reproduction condition changing unit changes a developing bias of the normal developing unit.   3. The image forming apparatus according to claim 2, wherein the regular developing means can select two developing biases which are | first developing bias |> | second developing bias |, and the color reproduction characteristic selecting means is vivid. The color reproduction condition changing unit selects the first development bias when the color reproduction characteristic selection unit selects the priority on vividness. An image forming apparatus comprising: selecting the second developing bias when the selection is made and priority is given to gradation.   4. The image forming apparatus according to claim 1, further comprising a color color separation processing device for performing color separation of color image data to be formed into color image data of the plurality of developing units. An image forming apparatus characterized in that the apparatus performs color separation by each color separation method corresponding to the developing bias.   4. The image forming apparatus according to claim 2, further comprising a color color separation processing device for performing color separation of the color image data to be formed into each color image data of the plurality of developing units. An image forming apparatus, wherein color separation is performed by a color separation method corresponding to the development bias selected based on whether the vividness selected by the reproduction characteristic selection unit is prioritized or whether gradation is prioritized.   6. The image forming apparatus according to claim 2, wherein the color reproduction characteristic selected by the color reproduction characteristic selection unit is selected based on a user instruction. Image forming apparatus.   6. The image forming apparatus according to claim 2, wherein the color reproduction characteristic selected by the color reproduction characteristic selection unit is selected based on color image data to be formed. Image forming apparatus.   8. The image forming apparatus according to claim 1, wherein the developing unit is disposed in a developing region so as to face the image carrier in a non-contact manner, and the toner is disposed in the developing region. An image forming apparatus comprising a toner carrier carried in a non-stationary state.   9. The image forming apparatus according to claim 8, wherein the toner carrier includes a plurality of electrodes arranged side by side at a predetermined interval, and a power source that applies a multiphase voltage to the electrodes. An image forming apparatus, wherein the toner is carried to a region facing the image carrier while being carried by a traveling wave electric field formed by a voltage applied between the electrodes.   9. The image forming apparatus according to claim 8, wherein the toner carrier includes a plurality of electrodes arranged at predetermined intervals and a power source for applying a multiphase voltage to the electrodes, and the surface of the toner carrier is A traveling wave electric field formed by a voltage applied between a plurality of electrodes by the power source and the surface movement of the toner carrier, and the toner on the toner carrier with the image carrier. An image forming apparatus transported to a facing area.   9. The image forming apparatus according to claim 8, wherein the toner carrier includes a plurality of electrodes arranged side by side at a predetermined interval, and a power source for applying a voltage to the electrodes, and the surface of the toner carrier is movable. The toner is carried in a non-stationary state by an oscillating electric field formed by a voltage applied between a plurality of electrodes by the power source, and the toner on the toner carrier is carried by the surface movement of the toner carrier. An image forming apparatus, wherein the image forming apparatus is conveyed to a region facing the body.   12. The image forming apparatus according to claim 1, wherein the plurality of developing units are four colors of cyan, magenta, yellow, and black, respectively. An image forming apparatus, wherein development is performed using the toner.

Images