JP2004287156A - Image forming device and its method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accelerate image formation when obtaining a full color image by superposing a plurality of developers on the surface of an image carrier, to improve color reproducibility while holding sufficient exposure light quantity, to prevent color mixing in a developing device, and to extend the life of the developer. <P>SOLUTION: The image forming device is constituted so as to obtain a full color toner image of four colors by respectively forming toner images on which two colors are superposed on 1st and 2nd photoreceptor drums 11, 12, and, in image transfer, superposing the two-color toner images formed on respective photoreceptor drums 11, 21 on a sheet of paper P. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus and an image forming method for forming a color image using a plurality of color developers.
[0002]
[Prior art]
In an image forming apparatus that obtains a color image by an electrophotographic method, in order to reduce the size of the apparatus, increase the process speed, or improve the alignment accuracy of each color, conventionally, a single photoconductor is used. There is an image forming apparatus that sequentially forms four color toner images of yellow (Y), magenta (M), cyan (C), and black (BK) to obtain a full-color image. (For example, refer to Patent Document 1).
[0003]
[Patent Document 1]
JP-A-5-265295 (pages 2, 3; FIG. 1)
In this method, a charging process, an exposure process, and a developing process are sequentially performed on a photoconductor for each color of toner, and the obtained color toner image is overlaid on a photoconductor or an intermediate transfer body. To obtain a full-color image.
[0004]
That is, in the image forming apparatus for obtaining a full-color image on the single photosensitive member, the toner images of the second and subsequent colors are subjected to an image forming process of charging, exposure and development from the already formed toner images. Thus, a toner image of the next color is formed. For this reason, for example, in the case of an image forming apparatus that obtains a color image using a powder toner, a sufficient amount of exposure cannot be obtained in the image forming process for the second and subsequent colors because the light transmittance of the toner layer is low. In order to solve this problem, it is necessary to use an exposure source in the infrared region for the exposure apparatus or to increase the exposure power extremely. In particular, when a full-color four-color toner image is superimposed on a single photoreceptor, in the fourth-color image forming step, exposure must be performed from the top of the toner layer of a maximum of three colors, and the exposure power However, there is a problem that sufficient color reproduction cannot be obtained even if is increased.
[0005]
In the case of an image forming apparatus that obtains a color image using a liquid developer, extremely fine toner particles having a submicron size are used. Although the absorption of each exposure from is small, and the color reproducibility of a full-color image is superior, performing the exposure step from the point where the toner layer is already formed inevitably reduces the amount of each exposure, In order to obtain a high-quality image with better color reproducibility, it is desired that the previously formed toner layer is as thin as possible.
[0006]
On the other hand, when a plurality of color toner images are superimposed on a single photoreceptor, the toner image formed on the photoreceptor earlier drops off after the next development, so that the second and subsequent colors are not developed in the developing device. In many cases, color mixing of toner cannot be avoided, and image output over a long period of time cannot be tolerated. Further, when a toner image of a plurality of colors is overlaid on a single photoreceptor and the toner layer is thickened, cracks are easily generated on the surface of the toner layer, the transferability is poor, and a clearer transfer image may not be obtained. Was.
[0007]
On the other hand, conventionally, a four-tandem tandem in which a color image is formed in one pass by using an image forming unit for forming a toner image for each color on each of four photosensitive members and arranging a plurality of image forming units on a sheet paper conveyance path. There is an image forming apparatus of a system. (For example, see Patent Document 2).
[0008]
[Patent Document 2]
JP-A-11-65308 (pages 4 to 6, FIG. 1)
However, although this (Patent Document 2) and the like use a four-tandem tandem system and are suitable for high-speed operation and excellent in reproducibility of each color, after forming four-color toner images on separate photoconductors, the four colors are separated. In this case, a high degree of misregistration correction is required at the time of transfer.
[0009]
[Problems to be solved by the invention]
In view of the above, the present invention has been made to solve the above-mentioned problems, and in the case of superimposing a plurality of developers on a photoreceptor, a decrease in color reproducibility due to a decrease in the amount of exposure or a deterioration in transferability due to cracks in a toner layer. An image forming apparatus that can easily prevent misregistration, obtain a high-quality color image, prevent deterioration of the developer due to color mixing, extend the life of the developer, and easily correct misalignment without impairing the speeding up. It is an object to provide an image forming method.
[0010]
[Means for Solving the Problems]
According to the present invention, as a means for solving the above problems, a first image holding member having an electrostatic latent image formed on a surface thereof, and a developer having a first brightness supplied to the first image holding member. A first image forming unit for forming a first developed image; and a second lightness developer supplying second developer to the first image carrier after forming the first developed image. A second image forming unit for forming an image, a second image holding member having an electrostatic latent image formed on the surface thereof, and supplying a third lightness developer to the second image holding member to form a third image holding member. A third image forming unit for forming a fourth developed image; and forming a fourth developed image by supplying a developer having a fourth brightness to the second image carrier after forming the third developed image. A fourth image forming unit, and the first and second developed images and the second image formed on the first image holding member. Said third and fourth developed images are formed on the lifting body is intended to provide a transfer device for multiplexing transferred to the transferred material.
[0011]
According to another aspect of the invention, there is provided a first image holding member having an electrostatic latent image formed on a surface thereof, and a developer having a first brightness supplied to the first image holding member. A first image forming unit for forming a first developed image, and after forming the first developed image, supplying a developer of a second brightness to the first image holding member to perform a second development. A second image forming unit for forming an image, a second image carrier on which an electrostatic latent image is formed on the surface, and a third lightness developer supplied to the second image carrier to supply a second brightness. A third image forming unit for forming a third developed image; and, after forming the third developed image, supplying a developer having a fourth brightness to the second image holding member to form a fourth developed image. A fourth image forming unit to be formed, and the first and second developed images and the second image formed on the first image holding member. A first side transfer device for multiplex-transferring the third and fourth developed images formed on the holding member to a first surface of a transfer material, and the first image centering on a transfer path of the transfer material A third image holding member facing the holding member and having an electrostatic latent image formed on a surface thereof, and supplying a developer having a fifth brightness to the third image holding member to form a fifth developed image A fifth image forming unit that forms a sixth developed image by forming a sixth developed image by supplying a developer having a sixth brightness to the third image holding member after forming the fifth developed image; A forming unit, a fourth image holding member that faces the second image holding member around a conveyance path of the transfer material, and has an electrostatic latent image formed on a surface thereof; and a fourth image holding member. A seventh image forming unit for supplying a developer having a seventh brightness to form a seventh developed image, and after forming the seventh developed image. An eighth image forming unit configured to supply an eighth brightness developer to the fourth image holding member to form an eighth developed image; and the fifth and fifth image forming units formed on the third image holding member. A second side transfer device for multiplex-transferring the sixth developed image and the seventh and eighth developed images formed on the fourth image holding member to a second surface of the transfer-receiving material; is there.
[0012]
Further, according to the present invention, as a means for solving the above problems, a developer having a first brightness is supplied to a first image holding member to form a first developed image, and then a developer having a second brightness is used. A first step of supplying a second developed image to form a second developed image; and supplying a third brightness developer to the second image holding member to form a third developed image. A second step of supplying a developer to form a fourth developed image, and a third step of multiple-transferring the first to fourth developed images onto a material to be transferred are performed.
[0013]
With the above configuration, the present invention improves the image quality by maintaining good color reproducibility and good transferability without impairing the speed at the time of forming a full-color image, and also prevents the color mixing of the toner to prolong the life of the developer. An image forming apparatus and an image forming method are provided which facilitates misalignment and further facilitates correction of misregistration.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the first embodiment shown in FIGS. FIG. 1 shows an image forming unit 10 of a full-color electrophotographic apparatus which is an image forming apparatus. A first station 100 and a second station 200 are arranged along the sheet transport path 8 of the sheet P, which is a transfer material of the image forming unit 10. Each of the stations 100 and 200 has a first photosensitive drum 11 as a first image holding member and a second photosensitive drum 21 as a second image holding member. The first photosensitive drum 11 and the second photosensitive drum have the same structure. For example, an organic or amorphous silicon photosensitive layer is formed on a conductive drum made of aluminum or the like. A protective layer made of a fluorine-based resin, a silicone-based resin, or the like.
[0015]
Around the first photosensitive drum 11, along the rotation in the direction of the arrow s1, magenta (M), which is the developer of the first brightness, and developer of the second brightness, which is lower in brightness than magenta (M). First and second image forming units 12M and 12BK for forming magenta (M) and black (BK) toner images, which are first and second developed images, using a certain black (BK) liquid toner Are arranged.
[0016]
Around the second photoconductor drum 21, along with the rotation in the direction of the arrow s2, yellow (Y), which is a third lightness developer, and a fourth lightness developer, which is lighter than yellow (Y), are used. Third and fourth image forming units 12Y and 12C for forming yellow (Y) and cyan (C) toner images, which are third and fourth developed images, using a certain cyan (C) liquid toner. Are arranged.
[0017]
Each of the image forming units 12M to 12C has a similar configuration except that the color of the liquid toner used is different. The first to fourth image forming units 12M to 12C include charging devices 13M to 13C each including a well-known corona charger or scorotron charger, and magenta (M) to cyan (C) modulated according to image information. Exposure devices 14M to 14C for selectively performing light irradiation corresponding to the light signal of the above, attenuating the potential of the exposed portions of the photosensitive drums 11 and 21 to form an electrostatic latent image, and accommodating liquid toner of each color. A bias voltage is applied to the developing rollers 16M to 16C for supplying a liquid developer to the surfaces of the photosensitive drums 11 and 12 to form a toner image, and a squeezing roller 17M for simultaneously performing fogging of the developed toner image and removing the solvent. To 17C.
[0018]
Each of the exposure devices 14M to 14C uses a laser optical system having a wavelength of 670 nm.
[0019]
The supply of the liquid toner to the developing rollers 16M to 16C and the discharge of the liquid toner from the developing devices 18M to 18C of the developing devices 18M to 18C are controlled by a pump and a liquid circulation system (not shown). The developing rollers 16M to 16C are metal rollers provided with a gap of about 120 μm on the surfaces of the photosensitive drums 11 and 12, and the cleaning rollers 19M to 19C are in contact with the developing rollers 16M to 16C.
[0020]
The liquid toner is obtained by dispersing toner particles having a volume average particle diameter of 0.8 μm containing a pigment component in an insulating hydrocarbon solvent, and is charged (here, positively charged) in the solvent. I have. The toner particles are made of a mixture of an acrylic resin (for example, a thermoplastic resin having a glass transition point of 45 ° C.) and a coloring pigment of magenta, yellow, cyan, or black and a charge control agent.
[0021]
The squeeze rollers 17M to 17C are metal rollers facing the surfaces of the first or second photosensitive drums 11 and 21 with a gap of about 50 μm, and are brought into contact with the blades 20M to 20C.
[0022]
Downstream of the first and second image forming units 12M and 12BK around the first photosensitive drum 11 and downstream of the third and fourth image forming units 12Y and 12C around the second photosensitive drum 21. First and second suction rollers 22, 23 for accelerating the drying of the toner image by sucking excess solvent in contact with the squeezed liquid toner image after development by the developing devices 18M to 18C are provided. Can be Downstream of the suction rollers 22 and 23, first and second drying devices 24 and 26 for supplying an air flow to remove the solvent almost completely, and for multiple transfer of the toner image from which the solvent has been removed to the paper P. And a photoreceptor cleaner 46, 47 for collecting residual toner on the photoreceptor drums 11, 21, and erase lamps 48, 49 for removing residual charges.
[0023]
The suction rollers 22, 23 are rollers having a two-layer structure in which a conductive sponge layer is provided on a hollow metal shaft, and penetrate fluid from the sponge surface to the inside of the hollow shaft. The drying devices 24 and 26 are provided with a gap of about 1 mm from the surfaces of the photoconductor drums 11 and 21, and 4 to 6 m from the surfaces of the photoconductor drums 11 and 21. ³ / Min.
[0024]
The transfer device 27 is a first and second intermediate transfer medium that comes into contact with a primary transfer position around the first and second photosensitive drums 11 and 21, respectively, and the first and second intermediate transfer media that rotate in the directions of arrows t1 and t2. The second intermediate transfer rollers 30 and 31 and the secondary transfer positions around the intermediate transfer rollers 30 and 31 via the paper conveyance path 8 contact the intermediate transfer rollers 30 and 31 with the photosensitive drums 11 and 21, respectively, so as to make pressure contact. An intermediate transfer roller that has pressure rollers 32 and 33 that rotate in the directions of arrows x1 and x2 and that transfers toner images formed on the photoconductor drums 11 and 21 by utilizing the adhesive force, pressure, and shear stress of toner particles; After the primary transfer to 30 and 31, the secondary transfer to the paper P is performed. An intermediate transfer cleaner downstream of the secondary transfer position around the intermediate transfer rollers 30 and 31 removes extraneous matter such as residual toner remaining on the surfaces of the intermediate transfer rollers 30 and 31 after the transfer of the toner image onto the paper P is completed. 34 and 36 are provided.
[0025]
As shown in FIG. 2, the intermediate transfer rollers 30 and 31 are formed by forming a silicone rubber elastic layer 38 having a thickness of about 200 μm on the surface of a metal hollow roller containing a heater 37 such as a halogen lamp. , 31 surfaces are maintained at about 80 ° C. The pressure rollers 32 and 33 are made of a metal hollow roller 41 having a built-in heater 40 composed of a halogen lamp or the like, the surface temperature is maintained at 120 ° C., and the pressure rollers 32 and 33 are located between the photosensitive drums 11 and 21 and the intermediate transfer rollers 30 and 31. The applied pressure is 10Kg / cm ² It is about.
[0026]
Further, the surface speed v2 of the intermediate transfer rollers 30, 31 is set slightly lower than the surface speed v1 of the photoconductor drums 11, 21 so that v2 / v1 = 0.98. During the primary transfer to the intermediate transfer rollers 30 and 31, pressure and shear stress are applied to the toner image.
[0027]
Next, the operation will be described. When the image forming process is started, first, in the first station 100, the first photosensitive drum 11 rotates in the direction of arrow s1, and at the same time, toner image formation by the first and second image forming units 12M and 12BK. An operation is performed. First, in the first image forming unit 12M, the surface of the first photosensitive drum 11 is uniformly charged to about +800 V by the charging device 13M. Next, the exposure device 14M selectively irradiates the exposure corresponding to the image information of magenta (M) corresponding to the input image information to the first photosensitive drum 11 to lower the potential of the image portion to about + 200V. Then, an electrostatic latent image corresponding to magenta (M) image information is formed on the first photosensitive drum 11.
[0028]
In the developing device 18M, the developing roller 16M rotates in the same direction as the first photosensitive drum 11 at a moving speed about twice as fast as that of the first photosensitive drum 11, and the gap region between the developing roller 16M and the surface of the first photosensitive drum 11 is A meniscus is formed by the magenta (M) liquid toner.
[0029]
At this time, a voltage of about +600 V is applied to the developing roller 16M, and when the electrostatic latent image passes through the meniscus area of the magenta (M) liquid toner between the first photosensitive drum 11 and the developing roller 16M, an image is formed. The electric field is formed in the direction from the developing roller 16M to the surface of the first photosensitive drum 11 in the portion, and in the direction from the surface of the first photosensitive drum 11 to the developing roller 16M in the non-image portion. Therefore, the toner particles in the positively charged magenta (M) liquid toner adhere to only the image area. As a result, a magenta (M) toner image, which is the first color, is first formed on the first photosensitive drum 11 after passing through the developing roller 16M.
[0030]
As a result, the potential of the image section rises to about + 300V. Next, a voltage of about +600 V is applied to the squeeze roller 17M. When the liquid toner image approaches the squeeze roller 17M, an electric field is formed in the direction from the surface of the first photosensitive drum 11 to the squeeze roller 17M in the non-image portion, and conversely, the first electric field is generated from the squeeze roller 17M in the image portion. An electric field is formed in a direction toward the photosensitive drum 11. As a result, the floating charged toner particles are collected in the non-image portion, and the toner particles forming the image are pressed against the surface of the first photosensitive drum 11 in the image portion.
[0031]
Further, the squeeze roller 17M rotates at a speed about three times as fast as the rotation of the first photosensitive drum 11, and the fluid squeezing effect acts, so that the squeeze roller 17M is mainly applied to the upper layer of the liquid toner image. Certain solvents are removed. As a result, the thickness of the liquid toner image having a size of 1 μm or more is reduced to half or less. The solvent and the floating toner collected from the surface of the first photosensitive drum 11 are scraped off by the blade 20M and collected by a collecting unit (not shown).
[0032]
Next, the second color black (BK) toner image is formed on the first photosensitive drum 11 in the same manner, and the black (BK) toner image is superimposed on the magenta (M) toner image. Is done. That is, the charging device 13BK charges the magenta (M) toner image on the surface of the first photosensitive drum 11 and forms an electrostatic latent image corresponding to the black (BK) image information by the exposure device 14BK. . At the time of exposure by the exposure device 14BK, the magenta (M) toner image shows a very high transmittance in a region having a wavelength of 620 nm or more. Is obtained. In the present embodiment, since a laser optical system having a wavelength of 670 nm is used for exposing the black (BK) image information, the amount of each exposure can be reduced by being hindered by the magenta (M) toner image. And a good electrostatic latent image can be obtained. Next, the magenta (M) and black (BK) toner images are superimposed on the first photosensitive drum 11 via the developing device 18BK.
[0033]
Thereafter, the suction roller 22 sucks excess solvent from the toner image on the first photosensitive drum 11 by the suction roller 22. At this time, a potential of about +800 V is applied to the surface of the suction roller 22 to prevent the toner image from transferring to the sponge surface of the suction roller 22. Next, the toner image is almost dried through the drying device 24. At the time of this drying, the drying speed can be reduced as compared with the conventional case where four toner images are overlaid on the same photosensitive drum.
[0034]
Thereafter, the two-color toner image of magenta (M) and black (BK) is applied to the first photosensitive drum 11 side by the pressure roller 32 at 10 kg / cm. ² The first intermediate transfer roller 30 is pressed against the surface of the first photosensitive drum 11 and conveyed at a speed v2 that satisfies v2 / v1 = 0.98 with respect to the surface speed v1 of the first photosensitive drum 11, and applies a pressing force and heat to the first intermediate transfer roller 30. The primary transfer is performed by further applying a shear stress to the action. During this primary transfer, a shear stress is applied between the first photosensitive drum 11 and the first intermediate transfer roller 30, so that the transfer efficiency of the toner image is dramatically improved. Next, the toner image on the first intermediate transfer roller 30 is secondarily transferred to the sheet P conveyed in the direction of arrow u by the action of the pressure and heat from the pressure roller 32, and the magenta (M) , Black (BK).
[0035]
After the primary transfer of the toner image to the first intermediate transfer roller 30 is completed, the residual toner image on the first photosensitive drum 11 is removed by the photosensitive member cleaner 46, and the residual charge is erased by the erase lamp 48. The image forming process is ended, and the image forming process is prepared for the next image forming process. After the completion of the secondary transfer to the sheet P, the first intermediate transfer roller 30 is cleaned by the intermediate transfer cleaner 34 to remove the deposits on the surface.
[0036]
In the second station 200, the yellow (Y) toner image is formed on the second photosensitive drum using the third image forming unit 12Y in the same manner as the two-color toner image formation on the paper P in the first station 100. Is formed, a cyan (C) toner image is formed on the yellow (Y) toner image using the fourth image forming unit 12C.
[0037]
Here, when the second photoconductor drum 21 is exposed by the exposure device 14C of the fourth image forming unit, a yellow (Y) toner image is formed on the surface of the second photoconductor drum 21; Since the toner image Y) shows a very high transmittance in the wavelength region of 670 nm, the exposure operation of cyan (C) by the exposure device 14C using the laser optical system having the wavelength of 670 nm A good electrostatic latent image can be obtained without reducing the amount of exposure for each image.
[0038]
Next, after the two-color toner image of yellow (Y) and cyan (C) formed on the second photosensitive drum 21 by the suction roller 23 and the drying device 26 of the second station 200 is dried, the action of pressing force and heat is performed. , And a two-color toner image is primarily transferred to the second intermediate transfer roller 31. Then, the two-color toner image on the second intermediate transfer roller 31 is conveyed from the first station 100 side in the direction of arrow u by the action of the pressure and heat of the pressure roller 33, and is already magenta (M) and black (BK). 2) is superimposed on the paper P on which the two-color toner image is formed and subjected to secondary transfer to complete a full-color toner image on the paper P.
[0039]
After the primary transfer of the toner image is completed, the residual toner image of the second photosensitive drum 21 is removed by the photosensitive member cleaner 47, and the residual charge is erased by the erase lamp 49. Further, after the completion of the secondary transfer to the paper P, the second intermediate transfer roller 31 has the intermediate transfer cleaner 36 removing the attached matter on the surface.
[0040]
The full-color toner image output on the paper P as described above had very good four-color overlap, good color reproducibility, and high image quality. In addition, the deterioration of the liquid toner due to the color mixture is reduced, and the service life is extended as compared with the related art.
[0041]
With the above configuration, in the present embodiment, the first station 100 and the second station 200 form toner images of two colors each, and then superimpose four colors on the paper P to form a full-color toner image. Have gained. Therefore, since only two color toner images are superimposed on each of the photoconductor drums 11 and 21, the toner image formed earlier is compared with the conventional case where four color toner images are superimposed on the same photoconductor drum. A good electrostatic latent image with sufficient exposure without using an exposure source in the infrared region or increasing the exposure power with little effect of reducing the exposure. And a high-quality color image with good color reproducibility can be obtained.
[0042]
Further, since only two color toner images are superimposed on each of the photosensitive drums 11 and 21, it is possible to shorten the image forming time in each of the stations 100 and 200 and to dry the toner images before transfer. The time required can be reduced, and the speed of full-color image formation can be increased.
[0043]
Further, since the color superposition at each of the stations 100 and 200 is two colors, the deterioration of the liquid toner due to the color mixture can be reduced as compared with the conventional apparatus for superimposing four colors, and the life of the liquid toner can be extended. can get. Further, as compared with the conventional apparatus in which four color toner images are formed on the same photosensitive drum, the image quality can be improved because the cracks in the toner layer can be significantly reduced. Furthermore, since the color transfer on the paper P at the time of the secondary transfer is performed in a state where the two colors are superimposed on each other, compared with the case where the four colors are separately superposed as in the conventional four-tandem system, Correction of misregistration at the time of transfer can be made much easier.
[0044]
Next, the present invention will be described with reference to a second embodiment shown in FIG. In the present embodiment, although the structure of the transfer device is different from that of the first embodiment, the rest is the same as the first embodiment. Therefore, the same reference numerals are used for the same parts as the first embodiment. The description is omitted.
[0045]
In the present embodiment, two-color toner images of magenta (M) and black (BK) and two colors of yellow (Y) and cyan (C) formed on the first and second photosensitive drums 11 and 21 are used. A transfer device 28 for multiplex-transferring the color toner image onto the sheet P is supported by first to third support rollers 51, 52, 53, and is a belt-shaped intermediate member that comes into contact with a primary transfer position around the photosensitive drums 11, 21. It has an intermediate transfer belt 54 as a transfer medium. The first and second support rollers 51 and 52 have heaters 56 and 57 built in metal hollow rollers, maintain the surface temperature of the intermediate transfer belt 54 at about 80 ° C., and hold the intermediate transfer belt 54 at about 10 kg. / Cm ² To the photosensitive drums 11 and 21. Further, the secondary transfer position of the intermediate transfer belt 54 is set at about 10 kg / cm ² A pressure roller 58 is provided which has a built-in heater 59 which is brought into contact with the pressure of 1.degree.
[0046]
The traveling speed v3 of the intermediate transfer belt 54 in the direction of arrow w is set slightly lower than the surface speed v1 of the photosensitive drums 11 and 21 so that v3 / v1 = 0.98. During the primary transfer from the toner image to the intermediate transfer belt 54, pressure and shear stress are applied to the toner image. Reference numeral 60 denotes an intermediate transfer belt cleaner.
[0047]
In the image forming process, a two-color toner image is formed from the second station 200 side. In the transfer process, first, the two-color toner image of yellow (Y) and cyan (C) on the second photosensitive drum 21 is added. The primary transfer to the intermediate transfer belt 54 is performed by further applying a shear stress to the action of pressure and heat. Next, the two-color toner image of magenta (M) and black (BK) on the first photosensitive drum 11 of the first station 100 is further subjected to a shearing stress by the action of pressure and heat to yellow (Y) and cyan ( The primary transfer is performed on the two-color toner image C) to the intermediate transfer belt 54 to obtain a full-color primary transfer toner image on the intermediate transfer belt 54. Thereafter, the full-color primary transfer toner image on the intermediate transfer belt 54 is secondarily transferred to the paper P traveling on the paper transport path 8 to complete the full-color toner image on the paper P.
[0048]
As in the first embodiment, the full-color toner image output on the sheet P as described above has very good overlap of four colors, good color reproducibility, high image quality, and Deterioration was reduced and the life was extended.
[0049]
With this configuration, similarly to the first embodiment, two color toner images are formed in the first station 100 and the second station 200, respectively, and then four colors are superimposed on the intermediate transfer belt 54. And a full-color toner image. Therefore, only the two color toner images are superimposed on each of the photoconductor drums 11 and 21, and there is almost no influence that the amount of exposure is reduced by the previously formed toner image. A good electrostatic latent image can be obtained without using various sources or an extremely large exposure power, and a high-quality color image with good color reproducibility can be obtained. I can do it.
[0050]
Further, the deterioration of the liquid toner due to the color mixture can be reduced, the service life of the liquid toner can be prolonged, and the image quality can be improved because cracks in the toner layer can be significantly reduced as compared with the conventional apparatus. Further, since the colors are also superimposed on the intermediate transfer belt 54 two by two, the misregistration correction can be made much easier as compared with the case where the four colors are separately superimposed as in the conventional four-tandem system. .
[0051]
Next, the present invention will be described with reference to a third embodiment shown in FIG. In this embodiment, two sets of the first and second stations used in the first embodiment are arranged symmetrically with respect to the paper transport path, and two colors are superimposed on both sides of the paper, thereby forming a full-color image. Therefore, the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.
[0052]
In the present embodiment, a third station 300 and a fourth station 400 are provided symmetrically with the first and second stations 100 and 200 via the paper transport path 8. The third station has a symmetrical structure with the first image forming unit 12M around the third photosensitive drum 111 rotated in the direction of the arrow s3, and forms a fifth image for forming a magenta (M) toner image. The sixth image forming unit 112BK has a symmetric structure with the forming unit 112M and the second image forming unit 12BK and forms a black (BK) toner image.
[0053]
The fourth station has a symmetric structure with the third image forming unit 12Y around the fourth photosensitive drum 121 rotated in the arrow s4 direction, and forms a seventh image on which a yellow (Y) toner image is formed. The eighth image forming unit 112C has a symmetric structure with the forming unit 112Y and the fourth image forming unit 12C and forms an image of cyan (C) toner.
[0054]
The fifth to eighth image forming units 112M to 112C are in contact with the charging devices 113M to 113C, the exposing devices 114M to 114C, and the cleaning rollers 119M to 119C, like the first to fourth image forming units 12M to 12C. Developing devices 118M to 118C having squeeze rollers 117M to 117C to be brought into contact with the developing rollers 116M to 116C and the blades 120M to 120C.
[0055]
Further, around the third and fourth photosensitive drums 111 and 112, the third and fourth suction rollers 122 and 123, the third and fourth drying devices 124 and 126, an intermediate member rotating in the directions of arrows t3 and t4. Transfer rollers 130 and 131, photoconductor cleaners 146 and 147, and erase lamps 148 and 149 are provided, respectively. Intermediate transfer cleaners 134 and 136 are provided around the intermediate transfer rollers 130 and 131.
[0056]
A two-color toner image of magenta (M) and black (BK) and a two-color toner image of yellow (Y) and cyan (C) are multiplex-transferred onto the first surface of the sheet P conveyed in the sheet conveying path 8. The intermediate transfer rollers 30 and 31 constitute a first side transfer device 70, and a two-color toner image of magenta (M) and black (BK), yellow (Y), and cyan (C) are formed on the second surface of the sheet P. The intermediate transfer rollers 130 and 131 for performing the multiple transfer of the two-color toner image form a second side transfer device 71. The intermediate transfer roller 30 and the intermediate transfer roller 130 are in pressure contact with each other via the paper transport path 8, and the intermediate transfer roller 31 and the intermediate transfer roller 131 are in pressure contact with each other via the paper transport path 8. The pressing force of each of the intermediate transfer rollers 30 to 131 on the photosensitive drums 11 to 121 is about 10 kg / cm. ² It is.
[0057]
With the start of the image forming process, the first and second image forming units 12M and 12BK sequentially apply magenta (M) and black (BK) to the first photosensitive drum 11 in the first station 100 and the third station 300. And at the same time, the magenta (M) and black (BK) toner images are sequentially superimposed on the third photosensitive drum 111 by the fifth and sixth image forming units 112M and 112BK.
[0058]
After that, the magenta (M) and black (BK) two-color toner images on the first and third photosensitive drums 11 and 111 are sucked by the suction rollers 22 and 122 to remove excess solvent. It is almost dried through 124. Next, the two-color toner images on the first and third photosensitive drums 11 and 111 are further pressed by the intermediate transfer rollers 30 and 130 to mutually press the intermediate transfer rollers 30 , 130 side. Further, the two-color toner image transferred onto the intermediate transfer rollers 30 and 130 is secondarily transferred to the first and second surfaces of the sheet P which is nipped and conveyed between the intermediate transfer rollers 30 and 130. Then, a two-color toner image of magenta (M) and black (BK) is formed.
[0059]
Similarly, the yellow (Y) and cyan (C) two-color toner images on the second and fourth photosensitive drums 21 and 121 are suctioned by the suction rollers 23 and 123 to remove excess solvent, and are dried by the drying devices 26 and 126. It is almost dried through. Then, the two-color toner images on the second and fourth photosensitive drums 21 and 121 are further pressed by the intermediate transfer rollers 31 and 131 against each other to apply a shearing force to the action of the pressing force and the heat to apply the intermediate transfer roller 31. , 131 side. Further, the two-color toner image transferred onto the intermediate transfer rollers 31 and 131 is secondarily transferred to both sides of the sheet P conveyed between the intermediate transfer rollers 31 and 131, and is already magenta (M) and black (BK). Then, a two-color toner image of yellow (Y) and cyan (C) is transferred from the top of the two-color toner image transferred, thereby completing a full-color toner image on both sides of the paper P.
[0060]
As in the first embodiment, the full-color toner images output on both sides of the sheet P as described above have very good overlap of four colors, good color reproducibility, high image quality, and color mixing. The deterioration of the liquid toner due to the above is reduced, and the service life is prolonged.
[0061]
With such a configuration, after forming toner images of two colors each in the first to fourth stations 100 to 400 symmetrically arranged via the paper conveyance path 8, the four colors are superimposed on the paper P. Thus, a full-color toner image is obtained. Therefore, as in the first embodiment, only the two color toner images are superimposed on each of the photoconductor drums 11 to 121, and there is almost the effect that the amount of exposure is reduced by the previously formed toner image. Without using an exposure source in the infrared region, or obtaining a good electrostatic latent image without significantly increasing the exposure power, it is possible to obtain a high-quality color image with good color reproducibility, Further, different images can be simultaneously formed on both sides of the sheet P, and the speed of full-color image formation can be further increased.
[0062]
Further, the deterioration of the liquid toner due to the color mixture can be reduced, the service life of the liquid toner can be prolonged, and the image quality can be improved because cracks in the toner layer can be significantly reduced as compared with the conventional apparatus. Further, compared with a case where four colors are separately superimposed as in the conventional four-unit tandem system, the displacement can be corrected much more easily.
[0063]
The present invention is not limited to the above-described embodiment, and can be changed without departing from the spirit thereof. For example, the developer may be a powder developer instead of a liquid developer. The combination of the two colors of the four-color developer is not limited, but it is desirable that the amount of each exposure is not reduced at the time of exposure in a subsequent image forming unit. The first station forms a toner image in the order of yellow (Y) and black (BK) and the second station forms a toner image in the order of magenta (M) and cyan (C) so as to increase the transmittance of the toner image to be formed. May be formed.
[0064]
Further, the wavelength of the optical system used in the exposure device of each image forming unit is not limited as long as it can transmit the toner image formed in advance. Further, the speed difference between the image carrier and the intermediate transfer medium for applying a shearing force to the toner image during transfer is also arbitrary.
[0065]
Further, for example, in the third embodiment, the opposing intermediate transfer rollers are pressed against each other via the paper transport path to press the intermediate transfer roller against the photosensitive drum, but the opposing intermediate transfer roller is shifted in position. Alternatively, a pressure roller may be provided to pressurize the intermediate transfer roller, or a toner image may be transferred by a transfer device using an intermediate transfer belt as described in the second embodiment.
[0066]
【The invention's effect】
As described above, according to the present invention, two different colors of developed images are formed on two image carriers, and then the four colors of developed images are superposed by transfer to obtain a full-color image. Therefore, since only the two-color developed images are formed on the image carrier in a superimposed manner, it is necessary to compensate for the reduction in the amount of exposure after the second color as in the conventional case of superimposing the four-color developed images. It is possible to obtain a good electrostatic latent image with a sufficient amount of exposure without using an exposure source in the infrared region or using a very large exposure power to obtain a high-quality color image with good color reproducibility. can get. Further, as compared with the case where the developed images of four colors are superimposed on the image holding member as in the related art, the time required for forming the image on each image holding member can be reduced, and the time required for drying the developed image can be reduced. Shortening can be achieved, and the speed of full-color image formation can be increased.
[0067]
Further, compared to a case where four developed images are superimposed on the same image carrier, the chance of mixing of the developer in the developing device can be reduced, and the life of the developer can be extended. Further, as compared with the case where the developed images of four colors are superimposed on the same image carrier, cracks generated in the stacked developers can be remarkably reduced, so that the image quality can be improved. On the other hand, when transferring, the developed image is transferred by superimposing two colors at a time, making it much easier to correct misregistration at the time of transfer than when the four colors are separately superimposed as in the conventional four-tandem system. Become.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an image forming unit of a full-color electrophotographic apparatus according to a first embodiment of the present invention.
FIG. 2 is a schematic sectional view illustrating an intermediate transfer roller and a pressure roller according to the first embodiment of the present invention.
FIG. 3 is a schematic configuration diagram illustrating an image forming unit according to a second embodiment of the present invention.
FIG. 4 is a schematic configuration diagram illustrating an image forming unit according to a third embodiment of the present invention.
[Explanation of symbols]
8 Paper transport path
10. Image forming unit
11 First photoconductor drum
12M to 12C: Image forming unit
13M to 13C: Charging device
14M-14C: Exposure equipment
16M-16C: Developing roller
17M ~ 17C ... Quizz roller
18M-18C: Developing device
20Y-20BK: Squeeze roller
21 ... second photosensitive drum
22, 23 ... Suction roller
24, 26 ... Drying device
27 ... Transfer device
30, 31 ... intermediate transfer roller
32, 33 ... pressure roller
100: Station 1
200 ... Second station

Claims (12)

A first image carrier on which an electrostatic latent image is formed,
A first image forming unit that supplies a developer of a first brightness to the first image holding member to form a first developed image;
A second image forming unit that supplies a developer of a second brightness to the first image holding member to form a second developed image after forming the first developed image;
A second image carrier on which an electrostatic latent image is formed on a surface;
A third image forming unit that supplies a developer of a third brightness to the second image holding member to form a third developed image;
A fourth image forming unit that supplies a developer of a fourth brightness to the second image holding member to form a fourth developed image after forming the third developed image;
Transfer for transferring the first and second developed images formed on the first image holding member and the third and fourth developed images formed on the second image holding member in multiple transfer to a transfer-receiving material And an image forming apparatus. The first to fourth developers are liquid developers, and the transfer device contacts the first image holding member under pressure to transfer the first and second developed images by non-electric field transfer. A roller-shaped first intermediate transfer medium for multiplex transfer onto a transfer material, and the third and fourth developed images are multiplexed onto the transfer material by non-electric field transfer by being brought into pressure contact with the second image carrier. 2. The image forming apparatus according to claim 1, further comprising a roller-shaped second intermediate transfer medium for transferring. The first intermediate transfer medium press-transfers the first and second developed images while applying a shear stress, and the second intermediate transfer medium applies the third and fourth images while applying a shear stress. 3. The image forming apparatus according to claim 2, wherein the developed image is transferred under pressure. The first to fourth developers are liquid developers, and the transfer device comes into pressure contact with the first image holding member and the second image holding member to perform the first to fourth development. 2. The image forming apparatus according to claim 1, further comprising a belt-shaped intermediate transfer medium that transfers a plurality of images onto the transfer material by non-electric field transfer. 3. The image forming apparatus according to claim 2, wherein the intermediate transfer medium transfers the first to fourth developed images under pressure while applying a shear stress. The image according to claim 1, wherein the brightness of the first developer is higher than the brightness of the second developer, and the brightness of the third developer is higher than the brightness of the fourth developer. Forming equipment. A first image carrier on which an electrostatic latent image is formed,
A first image forming unit that supplies a developer of a first brightness to the first image holding member to form a first developed image;
A second image forming unit that supplies a developer of a second brightness to the first image holding member to form a second developed image after forming the first developed image;
A second image carrier on which an electrostatic latent image is formed on a surface;
A third image forming unit that supplies a developer of a third brightness to the second image holding member to form a third developed image;
A fourth image forming unit that supplies a developer of a fourth brightness to the second image holding member to form a fourth developed image after forming the third developed image;
The first and second developed images formed on the first image carrier and the third and fourth developed images formed on the second image carrier are transferred to a first surface of a transfer-receiving material. A first side transfer device for performing multiple transfer to
A third image holding member that faces the first image holding member around a conveyance path of the transfer material and has an electrostatic latent image formed on a surface thereof;
A fifth image forming unit that supplies a developer having a fifth brightness to the third image holding member to form a fifth developed image;
A sixth image forming unit that supplies a developer having a sixth brightness to the third image holding member to form a sixth developed image after forming the fifth developed image;
A fourth image holding member that faces the second image holding member around a conveyance path of the transfer material and has an electrostatic latent image formed on a surface thereof;
A seventh image forming unit that supplies a developer having a seventh brightness to the fourth image holding member to form a seventh developed image;
An eighth image forming unit configured to supply an eighth brightness developer to the fourth image holding member to form an eighth developed image after forming the seventh developed image;
The fifth and sixth developed images formed on the third image holding member and the seventh and eighth developed images formed on the fourth image holding member are converted into a second image of the transfer-receiving material. An image forming apparatus comprising: a second side transfer device that performs multiple transfer onto a surface. The first to eighth developers are liquid developers,
A first intermediate transfer medium, wherein the first surface transfer device makes a pressure contact with the first image holding member and multiplex-transfers the first and second developed images to the material to be transferred by non-electric field transfer; A second intermediate transfer medium that press-contacts the second image holding member to multiplex-transfer the third and fourth developed images to the transfer-receiving material by non-electric field transfer;
A third intermediate transfer medium, wherein the second surface transfer device press-contacts the third image holding member to perform multiple transfer of the fifth and sixth developed images to the transfer target material by non-electric field transfer; A fourth intermediate transfer medium that makes a multiple transfer of the seventh and eighth developed images to the transfer target material by non-electric field transfer while being in pressure contact with the fourth image holding member;
The first pressure transfer medium and the third pressure transfer medium press each other via the transfer material,
8. The image forming apparatus according to claim 7, wherein the second pressure transfer medium and the fourth pressure transfer medium press each other via the transfer material. The first intermediate transfer medium press-transfers the first and second developed images while applying a shear stress, and the second intermediate transfer medium applies the third and fourth images while applying a shear stress. The developed image is pressure-transferred, and the third intermediate transfer medium press-transfers the fifth and sixth developed images while applying shear stress, and the fourth intermediate transfer medium applies shear stress. 9. The image forming apparatus according to claim 8, wherein the seventh and eighth developed images are transferred while being pressed. After supplying a developer having a first brightness to the first image holding member to form a first developed image, a developer having a second brightness is supplied to form a second developed image. Process and
After supplying a third brightness developer to the second image holding member to form a third developed image, a second brightness developer is supplied to form a fourth developed image. Process and
A third step of multiply transferring the first to fourth developed images onto a transfer material. The first to fourth developers are liquid developers, and the third step is a step of transferring the first to fourth developed images via an intermediate image holding member to the transfer target material by a non-electric field transfer step. The image forming method according to claim 10, wherein multiple transfer is performed. 12. The non-electric field transfer step is a pressure transfer step of transferring the first to fourth developed images to the material to be transferred while applying a shear stress by the intermediate image holding member. Image forming method.

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