JPH112927A - Image forming device and double-sided image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form double-sided images whose density and tones are regulated by making the rotational speed of a photoreceptor drum at the time of forming a toner image transferred to the rear surface of a transfer material lower than a moving speed at the time of forming the toner image transferred to the front surface of the transfer material. SOLUTION: A recording paper P is fed to a transferring area 14b, in a state where a color toner image of a front surface image carried on the photoreceptor drum 10 is synchronized with a toner image of a rear surface image carried on a toner image receptor 14a, by the drive of a timing roller 15c. At this time, the recording paper P is electrified to the same polarity as that of toner by a paper electrifier 14f and attracted to the toner image receptor 14a, to be fed to the transferring area 14b. At this time, a drive source for driving the drum 10 is controlled to make the rotational speed of the drum 10 at the time of forming the image on the rear surface lower than that at the time of forming the image on the front surface, so that the quantity of the toner stuck to the drum 10 become large.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer, and a facsimile, which form a toner image on an image bearing means, and transfer and fix the toner image on the image bearing means to a transfer material to form an image.
More particularly, the present invention relates to an image forming apparatus for forming an image on both sides of a transfer material and a double-sided image forming method.

[0002]

2. Description of the Related Art Conventionally, in double-sided image formation, a toner image formed on an image bearing means is transferred to one surface of a transfer material.
After fixing and temporarily storing the transfer material in the duplex paper feeder,
The transfer material is fed from the double-sided reversing sheet feeding device again in synchronization with the toner image formed on the image carrying means, and the toner image on the image carrying means is transferred and fixed to the other surface of the transfer material. The method of forming an image on both sides is adopted.

In this double-sided image forming apparatus, as described above, the transfer of the transfer material such as feeding to the two-sided reversing paper feeder or passing through the fixing device twice is performed, so that the transfer material transfer reliability is low.
This causes jams and wrinkles of the transfer material. On the other hand, according to JP-B-49-37538, JP-B-54-28740, JP-A-1-44457 and JP-A-4-214576, a toner image formed on an image bearing means is transferred to a transfer material. And the toner image formed on the image bearing means is once transferred to a toner image receiver, and then re-transferred to the back surface of the transfer material, and the toner images transferred to both surfaces of the transfer material are fixed at one time. By doing
One that forms an image on both sides of a transfer material has been proposed.

[0004]

However, in the double-sided image formation according to the above proposal, the image formation on the surface of the transfer material requires only one transfer from the image bearing means to the transfer material. The image formation on the back surface of the material is performed twice from the image carrying means to the toner image receiving body and from the toner image receiving body to the transfer material, so that the image density of the back side image is reduced. This is due to the fact that the transfer rate is not 100% at the time of transfer and the amount of toner adhered decreases. Also, the toner image 2
Gradation changes with each transfer, and good image formation cannot be performed.

[0005] Further, a color image has a new color tone problem as compared with a monochrome image. That is, since the order of superimposition of the color toners is reversed between the front and back of the transfer material, the color of the toner formed on the uppermost layer is emphasized,
The color tone is changed due to a decrease in the amount of adhesion due to the retransfer, which causes a problem that a good color image cannot be formed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus for forming a double-sided image having an adjusted image density and color tone.

[0007]

The above object can be attained by the following constitution.

(1) A first image carrying means for carrying a toner image, a toner image forming means for forming a toner image on the first image carrying means, and a toner image formed on the first image carrying means. A second image carrying means for carrying the transferred and transferred toner image on the surface, and transferring the toner image formed on the first image carrying means to the second image carrying means and a first surface of the transfer material. First transfer means, second transfer means for transferring the toner image transferred to the second image bearing means to a second surface of the transfer material opposite to the first surface, and toner transferred to the transfer material An image forming apparatus having a fixing unit for fixing an image, wherein the moving speed of the first image bearing unit when forming a toner image to be transferred to the second surface of the transfer material is transferred to the first surface of the transfer material. Slower than the moving speed of the first image carrying means when forming the toner image to be formed. An image forming apparatus.

(2) The moving speed of the first image carrying means when forming a toner image to be transferred to the second surface of the transfer material is determined by changing the moving speed of the first image carrying means when forming the toner image to be transferred to the first surface of the transfer material. (1) The image forming apparatus according to (1), wherein the moving speed of the first image carrier is 3 to 20% slower than the moving speed of the first image carrier.

(3) The image forming apparatus according to (1), wherein the moving speed of the first image bearing means is changed according to transfer conditions.

(4) Changing the image processing conditions between when forming a toner image to be transferred to the second surface of the transfer material and when forming a toner image to be transferred to the first surface of the transfer material. The image forming apparatus according to any one of (1) to (3).

(5) a second toner image forming step of forming a toner image to be transferred onto the second surface of the transfer material on the first image carrying means by the toner image forming means; and a second toner image forming step. Transferring the formed toner image onto the second image holding means, and transferring the toner image transferred by the toner image forming means onto the first surface of the transfer material opposite to the second surface. A first toner image forming step of forming the toner image on the transferring means,
Transferring the toner image transferred onto the second image holding means to the second surface of the transfer material, and transferring the toner image onto the first surface and the second surface of the transfer material. In the double-sided image forming method having a fixing step of fixing an image on a transfer material, when the same image is formed on the first surface and the second surface of the transfer material, the second toner image forming process is performed. 1
A two-sided image forming method, wherein the amount of toner adhering to the image carrying means is 3 to 15% larger than the amount of toner adhering to the first image carrying means in the first toner image forming step. Method.

[0013]

Embodiments of the present invention will be described below. In the following description, the first area in the transfer area will be described.
Place the surface of the transfer material on the side facing the image bearing means on the surface (first
Surface), the other side of the transfer material is referred to as a back surface (second surface),
An image transferred to the front surface of the transfer material is called a front image, and an image transferred to the back surface of the transfer material is called a back image.

First, an image forming process and each mechanism according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a color image forming apparatus showing an embodiment of the image forming apparatus of the present invention, FIG. 2 is a side cross-sectional view of the first image bearing means of FIG. 1, and FIG. FIG. 4 is a diagram illustrating a state of forming toner images on both sides and supply of a transfer material according to the first embodiment.

Photosensitive drum 10 as first image bearing means
For example, a transparent conductive layer on the outer periphery of a cylindrical substrate formed of a transparent member such as glass or transparent acrylic resin,
A photosensitive layer such as an a-Si layer or an organic photosensitive layer (OPC) is formed.

The photosensitive drum 10 is, as shown in FIG.
A guide pin 10P provided on a cover 503 which is sandwiched between a front flange 10a and a rear flange 10b and is attached to the front plate 501 of the apparatus main body.
1 and a plurality of guide rollers 1 that are supported by bearings and have a rear flange 10b attached to a rear plate 502 of the apparatus main body.
The photoreceptor drum 10 is held so as to be fitted to the outside of 0R. A gear 10G provided on the outer periphery of the rear flange 10b meshes with a driving gear G1, and the photosensitive member is clockwise indicated by an arrow in FIG. 1 in a state where the transparent conductive layer is grounded by power from a driving source (not shown). The drum 10 is rotated.

In the present embodiment, it is only necessary that the photoconductor layer of the photosensitive drum has an exposure light amount capable of giving an appropriate contrast. Therefore, the light transmittance of the transparent substrate of the photoreceptor drum in the present embodiment does not need to be 100%, and may have a characteristic such that a certain amount of light is absorbed when the exposure beam is transmitted. As the material of the translucent substrate, an acrylic resin, particularly one polymerized using methyl methacrylate monomer, has transparency, strength, accuracy,
Acrylic, fluorine used for other general optical members, etc.
Various translucent resins such as polyester, polycarbonate, and polyethylene terephthalate can be used. Further, as long as it has a light-transmitting property with respect to the exposure light, it may be colored. The light-transmitting conductive layer is made of indium-tin-oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, or a light-transparent metal thin film made of Au, Ag, Ni, Al, or the like. As a film forming method, a vacuum evaporation method, an active reaction evaporation method, various sputtering methods, various CVD methods, a dip coating method, a spray coating method, and the like are used. As the photoconductor layer, an amorphous silicon (a-Si) alloy photosensitive layer, an amorphous selenium alloy photosensitive layer, or various organic photosensitive layers (OPC) can be used.

Scorotron charger 1 as charging means
1. An exposure unit 12 as an image exposure unit and a developing unit 13 as a developing unit are used in an image forming process of each color of yellow (Y), magenta (M), cyan (C) and black (K). In the present embodiment, FIG.
With respect to the rotation direction of the photosensitive drum 10 indicated by the arrow,
Y, M, C, and K are arranged in this order.

As shown in FIG. 1, a scorotron charger 11 as a charging means for each color includes a support member 112 having a corona discharge electrode 111 formed of a sawtooth electrode and a U-shaped side plate 113 serving as a shield member. And a control grid 115 is further attached to the side plate 113. The control grid 115 is opposed to and close to the photosensitive drum 10 in a direction orthogonal to the moving direction of the photosensitive drum 10 as the first image holding means. A charging member to be attached. Other wire electrodes can be used as the corona discharge electrodes.

The scorotron charger 11 is charged by a corona discharge electrode 111 for performing a corona discharge having the same polarity as the toner, and a control grid 115 maintained at a predetermined potential with respect to the above-mentioned organic photosensitive layer of the photosensitive drum 10. The operation (in this embodiment, negative charging) is performed, and a uniform potential is applied to the photosensitive drum 10.

The exposure unit 12 serving as an image exposure unit for each color is arranged such that the exposure position on the photosensitive drum 10 is on the downstream side in the rotation direction of the photosensitive drum 10 with respect to the scorotron charger 11 for each color. , Are arranged inside the photosensitive drum 10.

The exposure units 12 for each color are respectively
LED (light emitting diode) as light emitting element of image exposure light
Are configured as an exposure unit in which a linear exposure element 12a in which a plurality of lenses are arranged in an array in parallel with the axis of the photosensitive drum 10 and a selfoc lens 12b as an equal magnification imaging element are mounted on a holder (not shown). Is done. The exposure unit 12 for each color is attached to a cylindrical holding member 20 together with the simultaneous transfer exposure device 12d and the uniform exposure device 12c, and the cylindrical holding member 20 is attached to the rear plate 502 of the apparatus main body.
And a guide pin 10P2 provided on a cover 503 attached to the front side plate 501.
By fixing P1 as a guide, the exposure unit 12, transfer simultaneous exposure unit 12d, and uniform exposure unit 12c for each color are integrally accommodated in the substrate of the photosensitive drum 10. As the exposure element, a linear element in which a plurality of light emitting elements such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array is used.

The exposure unit 12 performs image exposure on the photosensitive drum 10 based on image data of each color read by a separate image reading device and stored in a memory to form a latent image on the photosensitive drum 10. . The emission wavelength of the light emitting element used in this embodiment is preferably in the range of 680 to 900 nm, which is generally high in the transmittance of the Y, M, and C toners. A shorter wavelength which does not have sufficient transparency may be used.

The developing device 13 as a developing means for each color includes
For example, each has a thickness of 0.5 mm to 1 mm and an outer diameter of 15 to
A developing sleeve 131 which is a developer carrier made of a 25 mm cylindrical non-magnetic stainless steel or aluminum material
And a developing casing 138, and yellow (Y), magenta (M), cyan (C) and black (K) are provided inside.
Contains a one-component or two-component developer. The developing sleeve 131 includes a fixed magnet in which N and S magnetic poles are alternately arranged, and is stirred and mixed by the stirring screw 136, and is conveyed from the stirring unit by the supply roller 135 and supplied to the developing unit. And supply. At this time, the layer thickness of the two-component developer on the peripheral surface of the developing sleeve 131 is made of a magnetic material having a circular cross section of a magnetic material having a diameter of 3 to 10 mm and is uniformly pressed against the peripheral surface of the developing sleeve 131 with a predetermined load. It is regulated by a thin layer forming rod (not shown) as a thin layer forming member. The two-component developer that has passed through the developing unit is developed by a scraper (not shown) made of a plate-shaped elastic member such as SUS or urethane rubber provided by pressing one end of a long side of the belt in parallel with the developing sleeve 131. Sleeve 13
1 is conveyed to the stirring section by the supply roller 135, and is stirred and mixed by the stirring screw 136 so as to have a predetermined toner concentration.

In the developing section, the developing sleeve 131 is kept in a non-contact state with the photosensitive drum 10 by a contact roller (not shown) with a predetermined gap, for example, 100 μm to 1000 μm, in the rotating direction of the photosensitive drum 10. By applying a DC voltage of the same polarity as the toner (in this embodiment, a negative polarity) or a superimposed voltage of DC and AC to the developing sleeve 131 as a developing bias, Non-contact reversal development is performed on the exposed portion of the drum 10. At this time, the precision of the development interval needs to be about 20 μm or less in order to prevent image unevenness.

As described above, the developing device 13 applies the electrostatic latent image on the photosensitive drum 10 formed by the charging by the scorotron charger 11 and the image exposure by the exposure unit 12 to the photosensitive member in a non-contact state. The reversal development is performed with toner having the same polarity as the charging polarity of the drum 10 (in the present embodiment, the photosensitive drum is negatively charged, and the toner has a negative polarity).

An image read by an image sensor of an image reading apparatus separate from the apparatus or an image edited by a computer as an original image is temporarily stored in a memory as image data for each color of Y, M, C and K. Stored and stored.

A gear 10 provided on the rear flange 10b of the photosensitive drum 10 through a driving gear G1 by starting a photosensitive member driving motor (not shown) at the start of image recording.
G is rotated to rotate the photosensitive drum 10 in the clockwise direction indicated by the arrow in FIG. 1, and at the same time, the application of the potential to the photosensitive drum 10 is started by the charging action of the yellow (Y) scorotron charger 11.

After the photosensitive drum 10 is applied with a potential, the first color signal, that is, Y
Exposure by an electric signal corresponding to the image data is started, and an electrostatic latent image corresponding to the Y image of the original image is formed on the photosensitive layer on the surface by the rotational scanning of the drum.

The latent image is reversely developed in a non-contact state by a Y developing unit 13, and a yellow (Y) toner image is formed on the photosensitive drum 10.

Next, a potential is applied to the photosensitive drum 10 by the charging action of the magenta (M) scorotron charger 11 on the yellow (Y) toner image, and the second color signal of the M exposure unit 12 is applied. That is, exposure is performed by an electric signal corresponding to the M image data, and the magenta (M) toner image is superimposed on the yellow (Y) toner image by non-contact reversal development by the M developing unit 13. Formed.

By the same process, the cyan (C) toner image corresponding to the third color signal is further changed by the cyan (C) scorotron charger 11, the exposure unit 12 of C and the developing unit 13 of C to black ( The black (K) toner image corresponding to the fourth color signal is sequentially superimposed and formed by the scorotron charger 11 of K), the exposure unit 12 of K, and the developing unit 13 of K, and one rotation of the photosensitive drum 10 Within this time, a color toner image is formed on the peripheral surface (toner image forming means).

Exposure unit 1 for Y, M, C and K
Exposure of the organic photosensitive layer of the photosensitive drum 10 by 2 is performed from the inside of the drum through the transparent substrate described above. Therefore, the exposure of the images corresponding to the second, third, and fourth color signals is performed without any influence from the previously formed toner image, and is equivalent to the image corresponding to the first color signal. It is possible to form an electrostatic latent image. To stabilize the temperature in the photosensitive drum 10 and prevent the temperature from rising due to the heat generated by each exposure optical system 12, a material having good heat conductivity is used for the holding member 20, and a heater 201 is used at a low temperature. In the case of a high temperature, measures such as radiating heat to the outside through the heat pipe 202 can be suppressed to a level that does not cause a problem.

By the above-described image forming process, a superimposed color toner image serving as a back image is formed on the photosensitive drum 10 as the first image carrying means.
The superimposed color toner image of the upper back image is transferred to the transfer area 14.
b, the transfer roller 14c as a first transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied, the driving roller 14d and the driven roller 1
4e, and is collectively transferred onto a toner image receiver 14a as a second image carrying means provided close to or in contact with the photosensitive drum 10. At this time, for example, uniform exposure is performed by the simultaneous transfer exposure device 12d using a light emitting diode so that good transfer is performed.

The toner remaining on the peripheral surface of the photoconductive drum 10 after the transfer is subjected to static elimination by the photoconductive drum AC static eliminator 16, and then enters the cleaning device 19 or from the rubber material in contact with the photoconductive drum 10. Cleaning blade 1
In order to eliminate the history of the photoreceptor up to the previous print, static electricity is removed from the peripheral surface of the photoreceptor by, for example, exposure by a uniform exposure unit 12c before charging using a light emitting diode, and then the next surface is removed. Color image formation of the image is performed.

After the superimposed color toner image serving as the back image is transferred onto the toner image receiving member 14a, the superposed color image serving as the front image is formed on the photosensitive drum 10 in the same manner as the above-described color image forming process. A color toner image is formed. It is necessary to change the image data so that the front side image formed at this time is a mirror image of the back side image formed on the photosensitive drum 10.

The recording paper P, which is a transfer material, is fed from a paper feed cassette 15 which is a transfer material storage means to a feed roller 15.
a, is fed by the feed roller 15b, and is conveyed to the timing roller 15c.

As shown in FIG. 3, the recording paper P is carried by the timing roller 15c and is carried on the color toner image of the surface image carried on the photosensitive drum 10 and on the toner image receiver 14a. The image is fed to the transfer area 14b in synchronization with the color toner image of the back side image. At this time, the recording paper P is charged to the same polarity as the toner by a paper charger 14f composed of a corona discharger as a transfer material charging means, and is attracted to the toner image receiving member 14a to be transferred to the transfer area 14b
Is sent to By charging the paper with the same polarity as the toner, the toner is prevented from being attracted to the toner image on the toner image receiving member 14a or the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed.

In the transfer area 14b, a first voltage to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied.
The photoconductor drum 10 is transferred by the transfer device 14c as a transfer unit.
Are collectively transferred onto the surface of the recording paper P. At this time, the back surface image on the peripheral surface of the toner image receiver 14a is not transferred to the recording paper P but exists on the toner image receiver 14a. Next, the back side image on the peripheral surface of the toner image receiving body 14a is collectively recorded on a recording paper by a back side transfer unit 14g as a second transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied. It is transferred to the back surface of P.
In addition, at the time of transfer by the transfer device 14c, the photosensitive drum 10 is opposed to the transfer device 14c so that good transfer is performed.
A uniform exposure is performed by a transfer simultaneous exposure device 12d using, for example, a light emitting diode provided inside the device.

Since the toner images of the respective colors overlap each other, it is preferable that the toners in the upper layer and the lower layer of the toner layer are charged with the same charge amount and the same polarity in order to enable batch transfer. Accordingly, in the double-sided image formation in which the polarity of the color toner image formed on the toner image receiving body 14a is inverted by corona charging or the polarity of the color toner image formed on the photosensitive drum 10 is inverted by corona charging, Since the toner of the lower layer is not sufficiently charged to the same polarity, the transfer becomes unfavorable.

The reversal development is repeated on the photoreceptor drum 10, and the color toner images of the same polarity formed by superimposition are collectively transferred to the toner image receiving member 14a without changing the polarity, and then recorded without changing the polarity. Batch transfer to paper P is preferable because it contributes to improving the transferability of backside image formation. Also for the surface image formation, reversal development is repeatedly performed on the photosensitive drum 10 to collectively transfer color toner images of the same polarity formed by superimposition onto the recording paper P without changing the polarity.
It is preferable because it contributes to the improvement of transferability.

From the above, in forming a color image, the first transfer means is operated to form a color toner image on the front surface of the transfer material by using the above-described front and back surface image forming method. A two-sided image forming method for forming a color toner image on the back surface of the transfer material by operating the two transfer means is preferably employed.

Toner image receiver 1 as second image bearing means
4a is an endless rubber belt thickness 0.5 to 2.0 mm, the silicone rubber or urethane rubber ¹⁰ 10 10 ¹⁴
A semiconductive substrate having a resistance of Ω · cm, and a thickness of 5 μm to 5 μm as a toner filming prevention layer on the outside of the rubber substrate.
It has a two-layer structure with a fluorine coating of 0 μm. This layer also preferably has a similar semiconductivity. Instead of the rubber belt substrate, semiconductive polyimide or modified polyimide, polyester, polystyrene, polyethylene, polyethylene terephthalate, or the like having a thickness of 0.1 to 0.5 mm can also be used.

The recording paper P on which the color toner images are formed on both sides is subjected to a paper separation AC neutralizer 14h as a transfer material separating means.
, The toner is separated from the toner image receiving body 14a, and is conveyed to a fixing device 17 as a fixing unit including two rollers having heaters inside both rollers. By applying heat and pressure between the fixing roller 17a and the pressure roller 17b, the toner adhered to the front and back of the recording paper P is fixed, and the recording paper P on which double-sided image recording has been performed is sent by the paper discharge roller 18. And discharged to a tray outside the apparatus.

The toner remaining on the peripheral surface of the toner image receiver 14a after the transfer is transferred to the toner image receiver cleaning device 14i.
Cleaning. The toner remaining on the peripheral surface of the photoconductor drum 10 after the transfer is subjected to static elimination by the photoconductor drum AC static eliminator 16, and then enters the cleaning device 19 or is made of a rubber material that abuts on the photoconductor drum 10. Cleaning device 1 by cleaning blade 19a
9 and is collected by a screw 19b into a waste toner container (not shown). The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 19 is subjected to uniform exposure by the uniform charger 12c, and enters the next image forming cycle.

In the above-described double-sided image formation, the image formation on the back side is performed by the toner image from the photosensitive drum 10 as compared with the image formation on the front side which requires only one transfer from the photosensitive drum 10 to the front side of the recording paper P. Since the transfer is performed twice from the image receiving member 14a and the toner image receiving member 14a to the back surface of the recording paper P, the image density of the back surface image is reduced. This is due to the fact that the transfer rate is not 100% at the time of transfer and the amount of toner adhered decreases.

In order to solve this problem, in the present embodiment, the photosensitive drum 10 at the time of image formation on the back surface is used.
The driving source (not shown) for driving the photoconductor drum 10 is controlled so that the rotation speed (moving speed) of the photoconductor drum 10 is lower than the rotation speed of the photoconductor drum 10 when forming the image on the surface. That is, by reducing the rotation speed of the photoconductor drum 10, the amount of toner adhering to the photoconductor drum 10 during image formation on the back surface is increased. This makes it possible to compensate for a decrease in the amount of toner adhered by one-time transfer when forming an image on the back surface compared to when forming an image on the front surface, and to form a double-sided image with a uniform image density. The rotation speed of the developing sleeve 131 is the same between when forming an image and when forming an image on the back surface. That is, since the amount of adhered toner depends on the rotational speed ratio (moving speed ratio) between the photosensitive drum 10 and the developing sleeve 131, in the present embodiment, the developing sleeve is changed only by changing the rotational speed of the photosensitive drum 10. 1
The rotation speed of 31 is not changed. However, if the rotation speed ratio changes, the rotation speed of the developing sleeve 131 may be slightly changed. Further, the moving speed of the toner image receiving body 14a is always the same as the rotation speed of the photosensitive drum 10 in order to prevent the image from shifting.

Further, as a result of extensive studies by the present inventors, it has been found that the rotation speed of the photosensitive drum 10 when forming an image on the back surface is 3 to 20% slower than the rotation speed of the photosensitive drum 10 when forming an image on the front surface. Is preferred. That is,
When the same image is formed on the front surface and the back surface, the amount of toner adhering to the photoconductor drum 10 at the time of forming the image on the back surface is defined as:
It is preferable to increase the amount of toner adhering to the photosensitive drum 10 by 3 to 15% during the image formation on the surface.

The results of this study are shown in the following table. In addition,
The “photoconductor drum speed ratio” is a ratio of the front surface image formation to the back surface image formation, and is (photoconductor drum speed at front surface image formation) / (photoconductor drum speed at back surface image formation). ). “The ratio of the amount of toner adhering on the photosensitive drum” is the black (K) exposure unit 1
2 is the ratio of the toner adhesion amount per unit area on the photoconductor when a solid black latent image formed by exposing the photoconductor drum with an exposure amount of 60% of the maximum light amount is developed. (Amount of toner adhered during formation) / (amount of toner adhered during backside image formation). “Image on recording paper” represents the result of density measurement of the solid black image, and “O” indicates that the difference between the image density on the front side and the image density on the back side is 0.0.
5 indicates that the difference is indistinguishable by visual observation.
The following shows that a slight difference occurred.

[0050]

[Table 1]

Further, since the transfer condition (transfer rate) changes depending on the environment (temperature and humidity) and the recording paper P (thickness and resistance), the moving speed of the photosensitive drum 10 is changed according to the transfer condition. Is preferred. For this purpose, measurement of information on these environments (temperature and humidity) and detection of information on the recording paper P (thickness and resistance) are performed, and a transfer rate is predicted from the information on the environment and the recording paper P. What is necessary is just to control the moving speed of the photosensitive drum 10 according to the estimated transfer rate. Alternatively, the transfer rate from the photosensitive drum 10 to the toner image receiving member 14a, the transfer rate from the photosensitive drum 10 to the surface of the recording paper P,
Further, the transfer rate from the toner image receiving body 14a to the back surface of the recording paper P may be directly measured, and the moving speed of the photosensitive drum 10 may be controlled based on the measurement result.

In general, when an image of a document is copied (image formation) in an image forming apparatus, as shown in FIG. 4 showing an example of a digital image processing system for color reproduction, the document is scanned by a sensor such as a scanner. Is read (S1), and the read r, g, b image information is A / D
After the conversion (S2), shading correction (S3), matrix operation (S4), density conversion (S5), C,
M and Y signals are obtained. And masking, inking, U
By performing a CR (color processing) process (S6), C ', M',
The signals Y 'and K' are obtained, and are supplied as color signals to the printer P1 which is an image forming apparatus by performing [gamma] correction (S7) using a [gamma] correction curve and multi-value processing (S8). In addition,
When an image is formed using a signal from a computer or the like, the signal is directly input to S5 or S6. As described above, in the image forming apparatus, it is necessary to perform various kinds of image processing in order to form an optimum image by the image forming apparatus.

In the image forming apparatus according to the present embodiment, it is preferable to change the image processing conditions between when forming an image on the front side and when forming an image on the back side. That is, as in the present embodiment, since the image formation on the back surface is performed twice, the halftone tends to be broken (gamma is increased) and the characters are thickened. Therefore, in the present embodiment, γ correction (S7), which is one of the image processing,
Compared with the image formation on the front side, when forming the image on the back side, a low γ correction (a skewed γ correction curve is used. That is, the γ correction curve is different between the image formation on the front side and the image formation on the back side). ) And fine print processing (MTF filter is strengthened. That is, M
It is preferable to apply a different TF filter.

Further, in the image forming apparatus for forming a color image as in the present embodiment as compared with a monochrome image, a new color tone problem arises. That is, since the order of superimposition of the color toners is reversed between the front and back sides of the transfer material, the color of the toner formed on the uppermost layer is emphasized, and the color tone is changed due to a decrease in the amount of adhesion due to retransfer. ,
A problem arises in that good color image formation is not performed. For this reason, in the present embodiment, the setting of the masking parameters for color correction shown in S6 of FIG. 4 which is one of the image processing is performed at the time of forming the front surface image and the time of forming the rear surface image. It is preferable to change with.

That is, FIG. 5 shows a color toner image on the recording paper P formed by the image forming apparatus of this embodiment.
FIG. 5A is a diagram showing a color toner image formed on the front surface of the transfer material, and FIG. 5B is a diagram showing a color toner image formed on the back surface of the transfer material. When a color toner image is formed in the order of Y, M, C, and K by the image forming apparatus as shown in FIG. Since C, M, and Y are sequentially superimposed, a larger amount of the lowermost K toner adheres to the recording paper P. On the other hand, the back side image is shown in FIG.
As described above, the recording paper P is sequentially overlapped with M, C, and K with yellow (Y) down, so that K becomes the uppermost layer and black (K) is overemphasized, so that the K toner is reduced. Attach it to the recording paper P. The same applies to other Y, M, and C. As described above, it is preferable to change the image processing conditions (masking parameters) between the time of forming the front surface image and the time of forming the rear surface image. In addition, since the toner image is formed by two transfer of the toner image on the back surface, the color tone is different due to a decrease in the amount of adhesion. Therefore, it is preferable to perform color correction different from the front surface for adjusting the color tone in consideration of this point. .

Such color correction is performed in masking, inking, and UCR (color processing) processing (S6), and linear masking is generally performed. However, when performing advanced color correction,
Non-linear masking or look-up tables may be used.

[0057]

According to the present invention described in detail above, a double-sided image having an adjusted image density and color tone is formed.

[Brief description of the drawings]

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

FIG. 2 is a side cross-sectional view of a first image bearing unit of FIG.

FIG. 3 is a diagram illustrating a state of forming toner images on both sides and supply of a transfer material.

FIG. 4 is a diagram illustrating an example of a digital image processing system for color reproduction.

FIG. 5 is a diagram illustrating a superimposed color toner image.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum (first image carrier) 11 scorotron charger 12, 120 exposure unit 13 developer 14a toner image receiver (second image carrier) 14c transfer device (first transfer device) 14g back surface transfer device (first 2 transfer means) 17 Fixing device P Recording paper (transfer material)

Claims (5)

[Claims] A first image holding unit for holding a toner image; a toner image forming unit for forming a toner image on the first image holding unit; and a transfer of the toner image formed on the first image holding unit. And
A second image holding means for holding the transferred toner image on the surface, and a toner image formed on the first image holding means in the second image holding means.
A first transfer unit that transfers the image to the first surface of the transfer material, and the toner image that is transferred to the second image support unit is transferred to a second surface of the transfer material opposite to the first surface. An image forming apparatus comprising: a second transfer unit; and a fixing unit that fixes a toner image transferred to a transfer material, wherein the first image holding unit is used to form a toner image transferred to a second surface of the transfer material. Wherein the moving speed of the first image carrier is lower than the moving speed of the first image carrier when forming the toner image to be transferred onto the first surface of the transfer material. 2. The method according to claim 1, wherein the moving speed of the first image carrier when forming the toner image transferred to the second surface of the transfer material is controlled by changing the moving speed of the first image bearing means when forming the toner image transferred to the first surface of the transfer material. 2. The image forming apparatus according to claim 1, wherein the moving speed of the first image bearing unit is 3 to 20% lower than the moving speed. 3. The image forming apparatus according to claim 1, wherein a moving speed of said first image bearing means is changed according to a transfer condition. 4. The method according to claim 1, wherein an image processing condition is changed between when forming a toner image transferred to the second surface of the transfer material and when forming a toner image transferred to the first surface of the transfer material. The image forming apparatus according to claim 1. 5. The transfer material according to claim 2, wherein the toner image forming means forms the second transfer material.
A second toner image forming step of forming a toner image to be transferred to a surface on a first image carrying means, and a step of transferring the toner image formed in the second toner image forming step to a second image carrying means A first toner image forming step of forming a toner image to be transferred onto a first surface of the transfer material opposite to the second surface by a toner image forming means on a first image carrying means; Transferring the toner image formed in the image forming step to the first surface of the transfer material; transferring the toner image transferred on the second image holding means to the second surface of the transfer material; The toner images transferred on the first surface and the second surface of the transfer material are
A method for forming a same image on a first surface and a second surface of a transfer material, the method comprising:
The amount of toner adhering on the first image carrying means in the second toner image forming step is 3 to 3 times smaller than the amount of toner adhering on the first image carrying means in the first toner image forming step. A double-sided image forming method characterized by increasing by 15%.