JP2010048922A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that prevents, regardless of the type of paper, image failure such as a white spot caused during transfer to the back of the paper. <P>SOLUTION: In both-sided image formation in which images are formed on the front and back of paper, control is performed based on a correspondence between image data of the front and rear so that a transfer aiding agent is transferred to the surface of the paper being an area where the toner image is transferred on the corresponding back of the paper. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus capable of forming images on both sides of a sheet.

  When double-sided images are formed on both sides of a sheet, there is a case where a problem called “white bubble phenomenon” occurs at the time of transferring the back side. This will be described below with reference to the drawings.

  FIG. 13 is a diagram for explaining the white bubble phenomenon in the conventional example. At the time of back surface transfer, the image is heated by a fixing device in order to fix the toner image in the front surface image forming process. For this reason, in the heated paper, the transfer process is performed on the paper whose moisture content is decreased and whose electric resistance value is increased. When the toner pt formed on the intermediate transfer body 6 is transferred by a transfer electric field formed between the intermediate transfer body 6 by applying a transfer voltage to the transfer roller 9, an abnormality occurs in a rough portion of the fiber of the paper P. Dielectric breakdown occurs due to discharge ed. As a result, a part of the toner ptb cannot be transferred to the paper P, and the part is white.

  By suppressing the transfer voltage to a low voltage, the occurrence of dielectric breakdown can be suppressed. However, if the voltage is set to a low voltage, a necessary electric field is not formed and transfer unevenness occurs due to insufficient transfer charge.

It is effective to humidify the paper in order to return the increase in the resistance value of the paper on the back side. In the image forming apparatus disclosed in Patent Document 1, a humidifying roller containing moisture is provided in the double-sided conveyance path, and the paper after the surface is fixed by the humidifying roller is humidified to increase the resistance value. Is prevented.
JP 2002-287603 A

  However, in the image forming apparatus described in Patent Document 1, it is necessary to separately provide a humidifying roller, which causes a problem of an increase in cost, and it is difficult to control because the optimum humidifying amount differs for each paper type. There was a problem.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of preventing image defects such as white bubble generated at the time of back surface transfer without depending on the type of paper.

1. An image carrier on which an electrostatic latent image is formed based on image data;
A plurality of developing devices for developing the electrostatic latent image with toner or a transfer aid;
A transfer unit for transferring the developed toner image and transfer auxiliary agent to the paper;
A fixing unit for heating the paper on which the toner image and the transfer auxiliary agent are transferred;
A double-sided conveyance unit that conveys the heated paper in the fixing unit, reverses the paper, and then conveys the paper again to the transfer unit;
Control means;
An image forming apparatus having
The control means corresponds to a region on the front surface of the paper, on which the toner image is transferred to the back surface of the paper, based on the correspondence between the image data of the front surface and the back surface when forming a double-sided image for forming images on the front and back sides of the paper. An image forming apparatus that performs control so that a transfer auxiliary agent is transferred to a region directly behind.

2. The control means includes
2. The image forming apparatus according to 1 above, wherein the transfer auxiliary agent is transferred to an area on the surface of the paper where the toner image is not transferred.

3. The control means includes
3. The image forming apparatus according to item 1 or 2, wherein the transfer auxiliary agent is transferred to an area where a transfer amount of the toner image on the surface of the sheet is small.

4). An image carrier on which an electrostatic latent image is formed based on image data;
A plurality of developing devices for developing the electrostatic latent image with toner or a transfer aid;
A transfer unit for transferring the developed toner image and transfer auxiliary agent to the paper;
A fixing unit for heating the paper on which the toner image and the transfer auxiliary agent are transferred;
A double-sided conveyance unit that conveys the heated paper in the fixing unit, reverses the paper, and then conveys the paper again to the transfer unit;
Control means;
An image forming apparatus having
The image forming apparatus according to claim 1, wherein the control unit controls the transfer auxiliary agent to be transferred to the entire area of the surface of the paper when the double-sided image is formed on the front and back of the paper.

  5. 5. The image forming apparatus according to any one of 1 to 4, wherein the transfer auxiliary agent is transparent fine particles or transparent toner.

  6). 5. The image forming apparatus according to any one of 1 to 4, wherein the transfer auxiliary agent is a carrier in which a magnetic carrier core is coated with a resin.

7). The transfer aid transferred to the surface of the paper is not fixed to the paper by heating at the fixing unit,
A collecting means for collecting a transfer auxiliary agent remaining on the surface of the paper that has passed through the fixing unit;
7. The image forming apparatus according to 6, wherein the transfer auxiliary agent collected by the collecting unit can be reused by a developing device that develops the transfer auxiliary agent.

  According to the present invention, an object is to provide an image forming apparatus capable of preventing image defects such as white bubble occurring at the time of back surface transfer without depending on the type of paper.

  Although the present invention will be described based on an embodiment, the present invention is not limited to the embodiment.

[Image forming apparatus]
FIG. 1 is a diagram illustrating a main part of an image forming apparatus 100 according to the present embodiment.

  The image forming apparatus 100 is called a tandem type color image forming apparatus, and includes a plurality of sets of image forming units 10S, 10Y, 10M, 10C, and 10K, a belt-shaped intermediate transfer belt 6, a paper feeding device 20, and a fixing device. 30 or the like.

  An image reading unit 110 is installed on the upper part of the image forming apparatus 100. The document placed on the document table is scanned and exposed by the optical system of the document image scanning exposure apparatus of the image reading unit 110 and read by the line image sensor. The analog signal photoelectrically converted by the line image sensor is subjected to analog processing, A / D conversion, shading correction, image compression processing, etc. in the control means, and then input to the exposure units 3S, 3Y, 3M, 3C, and 3K. The

  In the specification of the present application, the constituent elements are collectively indicated by a reference numeral in which the alphabetic suffix is omitted, and when referring to individual constituent elements, S (transparent), Y (yellow), M (magenta), Reference numerals with subscripts C (cyan) and K (black) are used.

  Image forming means 10S for forming an image of transparent toner (S) as a transfer aid, image forming means 10Y for forming a yellow (Y) image, image forming means 10M for forming a magenta (M) color image, The image forming means 10C for forming a cyan (C) color image and the image forming means 10K for forming a black (K) color image are respectively disposed around a drum-shaped photoconductor 1 as an image carrier. It has a strip electrode 2, an exposure unit 3Y, a developing device 4, and a cleaning unit 5 (reference numerals are omitted for Y, M, C, and K).

  The photoreceptor 1 is composed of an organic photoreceptor in which a photosensitive layer made of a resin containing an organic photoconductor is formed on the outer peripheral surface of a drum-shaped metal substrate, and the width direction of the sheet P to be conveyed (see FIG. 1 in a state extending in a direction perpendicular to the paper surface. Examples of the resin constituting the photosensitive layer include polycarbonate. In the embodiment shown in FIG. 1, the configuration example using the drum-shaped photoconductor 1 has been described. However, the present invention is not limited to this, and a belt-shaped photoconductor may be used.

  The developing device 4 includes a two-component developer composed of a transparent toner (S), yellow (Y), magenta (M), cyan (C), and black (K), each having a small particle diameter toner and a carrier. To do. As a two-component developer, a carrier in which a ferrite is used as a core and an insulating resin is coated around the carrier; a toner including a polyester, a colorant such as a pigment or carbon black, a charge control agent, silica, titanium oxide, and the like; Consists of. The carrier has a particle size of 10 to 50 μm, a saturation magnetization of 10 to 80 emu / g, and the toner has a particle size of 4 to 10 μm. The charging characteristics of the toner are negative charging characteristics, and the average charge amount is −20 to −60 μC / g. As the two-component developer, a mixture of these carrier and toner so that the toner concentration is 4 to 10% by mass is used.

  The transparent toner will be described. A charge control agent and a low molecular weight polypropylene are added to an acrylic resin and melted and kneaded, and then pulverized and classified to prepare transparent fine particles having a predetermined particle diameter, and hydrophobic silica fine particles are added to and mixed with this to use as a transparent toner.

  Other examples of transparent fine particles include polymethacrylic acid methyl acrylate resin fine particles, acrylic styrene resin fine particles, polymethyl methacrylate resin fine particles, silicon resin fine particles, polystyrene resin fine particles, polycarbonate resin fine particles, benzoguanamine resin fine particles, melamine Resin fine particles, polyolefin resin fine particles, polyester resin fine particles, polyamide resin fine particles, and polyimide resin fine particles.

The intermediate transfer belt 6 that is an intermediate transfer member is rotatably supported by a plurality of rollers. The intermediate transfer belt 6 is an endless belt having a volume resistance of 10 ⁶ to 10 ¹² Ω · cm. For example, polycarbonate (PC), polyimide (PI), polyamideimide (PAI), polyvinylidene fluoride (PVDF), tetrafluoroethylene -It is comprised with resin materials, such as ethylene copolymer (ETFE), and thickness is about 50-200 micrometers.

The intermediate transfer belt 6 is an endless belt having a volume resistance of the order of 10 ⁶ to 10 ¹² Ω · cm. For example, polycarbonate (PC), polyimide (PI), polyphenylene sulfide (PPS) polyamide imide (PAI), polyvinylidene fluoride (PVDF), etrafluoroethylene-ethylene copolymer (ETFE) and other resin materials, fluororesins, EPDM, NBR, CR, polyurethane and other rubber materials such as carbon are dispersed or ionic A material containing a conductive material is used, and the thickness is set to about 50 to 200 μm in the case of a resin material and about 300 to 700 μm in the case of a rubber material.

  The toner images of the respective colors formed on the photoreceptor 1 by the image forming units 10S, 10Y, 10M, 10C, and 10K are sequentially transferred (primary transfer) by the primary transfer roller 7 onto the rotating intermediate transfer belt 6 to be combined. A colored image is formed. On the other hand, the residual toner is removed by the cleaning portions 5 of the respective colors on the photoconductors 1Y, 1M, 1C, and 1K after image transfer.

  The paper P stored in the paper storage unit (tray) 21 of the paper supply device 20 is supplied by the first paper supply unit 22, and is supplied with paper supply rollers 23, 24, 25A, 25B, registration rollers (second paper supply). Part) 26 and the like, and conveyed to the secondary transfer roller 9 to transfer the color image onto the paper P (secondary transfer).

  Note that the three-stage paper storage units 21 arranged vertically in the vertical direction below the image forming apparatus 100 have substantially the same configuration, and thus are given the same reference numerals. The three-stage paper feeding units 22 are also given the same reference numerals because they have almost the same configuration. The paper storage unit 21 and the paper supply unit 22 are collectively referred to as a paper supply device 20.

  The paper P on which the color image is transferred is sandwiched by the fixing device 30 functioning as a “fixing unit”, and the color toner image (or toner image) on the paper P is fixed by applying heat and pressure. The sheet P is fixed on the sheet P, is nipped and conveyed by the conveyance roller pair 37, is discharged from the sheet discharge roller 27 provided in the sheet discharge conveyance path, and is placed on a sheet discharge tray 90 outside the apparatus.

  On the other hand, after the color image is transferred to the paper P by the secondary transfer roller 9, the residual toner is removed by the cleaning unit 61 from the intermediate transfer belt 6 from which the paper P is separated by curvature.

  In the “double-sided mode” in which images are formed on both sides of the paper P, the image formed on the front surface of the paper P (the front face: also referred to as the first side) is fixed, and then the paper P is fed by the branch plate 29. The paper is branched from the paper discharge conveyance path, introduced into the double-sided conveyance path 28, turned upside down, and conveyed again from the paper feed roller 25B. On the paper P, images of each color are formed on both sides by the image forming means 10Y, 10M, 10C, and 10K (also referred to as the second side), heated and fixed by the fixing device 30, and discharged to the outside by the paper discharge roller 27. Is done. The double-sided conveyance path 28, the branch plate 29, etc. function as “double-sided conveyance means”.

  In the above description, the example in which the image forming unit 10S of the transfer auxiliary agent is arranged on the most upstream side has been described. However, the present invention is not limited to this, and the image forming unit 10S may be arranged on the downstream side of the other image forming units 10. Good.

[Control block]
FIG. 2 is a control block diagram of the image forming apparatus 100 according to the present embodiment. The CPU 101 controls the overall operation of the image forming apparatus 100 and is connected to a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and the like via a system bus 109. The CPU 101 reads out various control programs stored in the ROM 102, develops them in the RAM 103, and controls the operation of each unit. The CPU 101 functions as a “control unit”.

  In addition, the CPU 101 executes various processes according to the program expanded in the RAM 103, stores the processing results in the RAM 103 and displays them on the operation display unit 105. Then, the processing result stored in the RAM 103 is stored in a predetermined storage destination. The ROM 102 stores programs, data, and the like in advance, and this recording medium is composed of a magnetic or optical recording medium or a semiconductor memory.

  The RAM 103 forms a work area that temporarily stores data processed by various control programs executed by the CPU 101.

  The HDD 104 has a function of storing image data of an original image obtained by reading by the image reading unit 106 and storing output image data and the like.

  The operation display unit 105 enables various settings. The operation display unit 105 has, for example, a touch panel format, and the user can set conditions regarding color printing and monochrome printing and the basis weight of the paper P loaded in the cassette 20 by inputting through the operation display unit 105. it can. Various kinds of information such as network setting information are displayed on the operation display unit 105.

  The print controller 110 includes a network I / F and receives a print job from an external PC or the like connected through the network. The received print job is converted by the print controller 110 into image data in a data format that can be formed by the image forming apparatus 100 in a predetermined page description language, and temporarily stored in the HDD 104 together with control data included in the print job. Or sent to the image processing unit 107.

  The control data is also called a job header. The control data includes information on the duplex mode or simplex mode, the number of copies, the number of pages per part, the size and basis weight of the paper used for output (image formation). Data, full color or monochrome mode information, and the like.

  The image forming unit 10 receives the image data processed by the image processing unit 107 and forms an image on the paper P.

[Effect of surface image on white bubble phenomenon]
The relationship between the white bubble phenomenon and the surface image of the first surface will be described with reference to FIGS. FIG. 3 is a schematic diagram showing a normal image b10 and a white petite image b11 when an image is formed on the paper using image data of the same halftone (intermediate density). When the paper P is held on the back side, the moisture content of the paper P is reduced by heating by the fixing device 30 at the time of fixing to the front surface. When the resistance of the paper P is increased, the potential difference generated on both sides of the paper P during transfer is increased. Slight abnormal discharge (dielectric breakdown) occurs in the sparse part of the paper fibers, and the abnormal discharge changes the polarity of the toner, making transfer impossible. As a result, a white small image b11 is generated as shown in FIG. On the other hand, such a rise in resistance value does not occur on the surface, so that a white image is not generated and the normal image b10 is output.

  FIG. 4 is a diagram for explaining the influence of the image on the front surface on the white bubble phenomenon occurring on the back surface. In FIG. 4A and FIG. 4B, image formation is performed based on the same half-tone image data (same as in FIG. 3) for the back side, but the front side is the same as in FIG. The front surface a1 is blank, and the front surface a2 in FIG. 4B is different from the alphabet letter K.

  As shown in FIG. 4, the white bubble phenomenon occurs over the entire back surface b1 of FIG. 4A, but the back surface b2 of FIG. 4B corresponds to the letter K on a part of the front surface a2. With respect to the position, the white bubble phenomenon does not occur and the transfer is performed normally.

  This is because the toner image is formed on the front surface, and as a result, the sparse part of the paper fiber also has a toner layer, so that it is difficult for abnormal discharge to occur during transfer of the back surface. In the present embodiment, control for preventing the occurrence of the white bubble phenomenon is performed based on such a phenomenon. This will be described below.

[Control flow]
FIG. 5 is an explanatory diagram of a control flow performed by the image forming apparatus 100 according to the present embodiment. The control flow is executed by the CPU 101 functioning as control means.

  In step S11 of FIG. 5, a print job is acquired from an external PC or the like. In step S12, by referring to the job header of the print job acquired in step S11, it is determined whether or not the print job is in the duplex mode. If the duplex mode is selected (step S12: Yes), the transfer area of the transfer auxiliary agent is calculated in the subsequent step S13.

[Calculation of transfer area]
FIG. 6 is a diagram illustrating a subroutine of step S13 in the present embodiment. In step S131, front side image data and back side image data are acquired.

  In step S132a, based on the back side image data acquired in step S131, (1) the area directly behind the area where the toner image is transferred to the back side of the sheet is set as the area where the transfer auxiliary agent is transferred.

A specific example will be described with reference to FIGS. FIG. 10 is a diagram illustrating an example of image data on the front surface and the back surface. In the image data on the surface, a low density letter I and a higher density letter K are arranged in the center. In the back side image data, a halftone rectangle r is arranged on the upper side as shown in FIG. FIG. 11 is a diagram illustrating a region to which the transfer auxiliary agent determined based on the correspondence relationship between the image data on the front surface and the back surface illustrated in FIG. 10 is transferred.
FIG. 11A shows an example of a region Sa in which the transfer auxiliary agent is transferred to the surface of the paper determined by the subroutine shown in FIG. The area Sa in the figure corresponds to the rectangle r of the image data on the back surface in FIG.
FIG. 11B shows an example of a region Sb in which the transfer auxiliary agent is transferred to the surface of the paper determined by a subroutine shown in FIG. 7 (described later).
FIG. 11C shows an example of the region Sc for transferring the transfer auxiliary agent to the surface of the paper determined by the subroutine shown in FIG. 8 (described later).
FIG. 11D shows an example of a region Sd in which the transfer auxiliary agent is transferred onto the surface of the paper, which is determined by a subroutine shown in FIG. 9 (described later).

  Returning to the description of the control flow in FIG. In step S14, based on the transfer area of the transfer auxiliary agent calculated in step S13 of the paper P (for example, area Sa in FIG. 11A) and the surface image data included in the print job acquired in step S11, Y An image is formed on the surface of the paper P by the M, C, and K toners and the transparent toner S as a transfer auxiliary agent.

  In step S15, image formation is performed with Y, M, C, and K toners based on the back side image data.

  According to the present embodiment, at the time of back surface transfer, since the transfer auxiliary agent is previously transferred to the surface corresponding to the back surface image, it is possible to prevent the occurrence of a white bubble phenomenon due to abnormal discharge. Further, since the transfer auxiliary agent is used, it is possible to prevent the occurrence of abnormal discharge without depending on the type of paper.

[Modification]
First to third modifications of the subroutine of step S13 will be described based on FIGS. 7 to 9 and FIG. Except for the subroutine shown in the figure, the embodiment is the same as the embodiment shown in FIGS.

In the “first modified example” shown in FIG. 7, the area on the front surface that satisfies the following (1) and (2) is transferred to the area where the transfer auxiliary agent is transferred, based on the back surface image data acquired in step S131b. Set to.
(1) The area directly behind the area where the toner image is transferred to the back side of the paper (2) The area where the front image is not formed Under the conditions of the image data shown in FIG. FIG. 11B shows a region Sb where the transfer auxiliary agent is transferred to the surface of the paper.

  According to this embodiment, it is possible to prevent the occurrence of abnormal discharge without depending on the type of paper, and since the transfer auxiliary agent is used only in the necessary area, the transfer auxiliary agent is used in an appropriate amount. Can be

In the “second modified example” shown in FIG. 8, the area on the front surface that satisfies the following (1) and (2) is transferred to the area where the transfer auxiliary agent is transferred based on the image data on the back surface acquired in step S131c. Set to.
(1) An area directly behind the area where the toner image is transferred to the back side of the paper. (2) An area where the image density of the front image is below a predetermined value. Under the conditions of the image data shown in FIG. FIG. 11C shows the region Sc determined by the above-described process in which the transfer auxiliary agent is transferred to the surface of the paper. In the example shown in the figure, the predetermined value of (2) is set between the character I of the low density portion and the character K of the higher density portion in FIG. This is because there is a possibility that the effect of suppressing abnormal discharge is insufficient in the area where the transfer amount of the toner image is small on the surface. It becomes possible to prevent the occurrence of discharge.

  According to this embodiment, it is possible to prevent the occurrence of abnormal discharge without depending on the type of paper, and since the transfer auxiliary agent is used only in the necessary area, the transfer auxiliary agent is used in an appropriate amount. Can be

  In the “third modified example” shown in FIG. 9, the entire surface area is set as an area to which the transfer auxiliary agent is transferred in step S132d.

  FIG. 11D shows a region Sd to which the transfer auxiliary agent is transferred onto the surface of the paper determined by the subroutine in the third modification.

  According to the present embodiment, since the transfer auxiliary agent is transferred to the entire surface area, it is possible to more stably prevent occurrence of abnormal discharge without depending on the type of paper.

[Other Embodiments]
FIG. 12 is a diagram illustrating the periphery of the collection device 40 of the image forming apparatus 100 according to another embodiment. In the image forming apparatus 100 shown in the figure, a carrier in which a magnetic carrier core is coated with a resin is used as a transfer aid. Except for the configuration shown in the figure, the embodiment is the same as the embodiment shown in FIGS.

  After the toner image is formed on the back surface of the paper P and heated by the fixing device 30 to be fixed on the paper, the transfer auxiliary agent transferred and adhered to the surface of the paper P is recovered by the recovery device 40.

  The collection device 40 includes a rotating brush 41, a metal rod 42, a scraper 43, a conveying screw 44, and the like.

  The rotating brush 41 is made of conductive acrylic, and is in pressure contact with the lower side of the paper P being conveyed (the image forming surface on the surface of the paper P). The rotating brush is rotated in the forward direction in the same direction as the transport direction of the paper P by driving means (not shown). That is, it rotates counterclockwise in the figure.

  The metal rod 42 is made of a permanent magnet such as a ferrite magnet, and a magnetic carrier collected from the paper P by the rotating brush 41 is attached thereto. The metal rod 42 is rotated in the clockwise direction in the drawing by a driving means (not shown). The magnetic carrier attached to the surface is peeled off by the scraper 43 in contact with the surface of the metal rod 43 and falls downward. The magnetic carrier falls downward and is conveyed to the rear side in the figure by a conveyance screw formed of a spiral screw and collected in a collection container (not shown). The magnetic carrier as a transfer aid collected in the collection container can be reused in the developing device 4S.

  Note that the recovery screw may be extended to the developing device 4S without providing a recovery container, and the conveyed magnetic carrier may be automatically returned to the developing device 4S.

  According to the present embodiment, at the time of back surface transfer, since the transfer auxiliary agent is previously transferred to the surface corresponding to the back surface image, it is possible to prevent the occurrence of a white bubble phenomenon due to abnormal discharge. Furthermore, since the transfer auxiliary agent is collected and reused, the amount of transfer auxiliary agent used can be reduced, and the running cost can be reduced.

1 is a diagram illustrating a main part of an image forming apparatus 100 according to an embodiment. 2 is a control block diagram of the image forming apparatus 100 according to the present embodiment. FIG. FIG. 6 is a schematic diagram showing a normal image b10 and a white small image b11 when an image is formed on a sheet with the same image data. It is a figure explaining the influence of the image of the surface with respect to the white bubble phenomenon generate | occur | produced on a back surface. It is explanatory drawing of the control flow which the image forming apparatus 100 in this embodiment performs. It is a figure explaining the subroutine of step S13. It is a figure explaining the 1st modification of the subroutine of Step S13. It is a figure explaining the 2nd modification of the subroutine of Step S13. It is a figure explaining the 3rd modification of a subroutine of Step S13. It is a figure which shows the example of the image data of a front surface and a back surface. It is a figure which shows the area | region which transfers the transfer adjuvant determined based on the correspondence of the image data of FIG. It is a figure which shows the collection | recovery apparatus 40 periphery of the image forming apparatus 100 which concerns on other embodiment. It is a figure explaining the white bubble phenomenon in a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Band electrode 3 Exposure part 4 Developing apparatus 6 Intermediate transfer belt 10 Image forming part 20 Paper feeding apparatus 30 Fixing apparatus 100 Image forming apparatus 110 Image reading part S Transparent toner 40 Collection | recovery apparatus

Claims (7)

An image carrier on which an electrostatic latent image is formed based on image data;
A plurality of developing devices for developing the electrostatic latent image with toner or a transfer aid;
A transfer unit for transferring the developed toner image and transfer auxiliary agent to the paper;
A fixing unit for heating the paper on which the toner image and the transfer auxiliary agent are transferred;
A double-sided conveyance unit that conveys the heated paper in the fixing unit, reverses the paper, and then conveys the paper again to the transfer unit;
Control means;
An image forming apparatus having
The control means corresponds to a region on the front surface of the paper, on which the toner image is transferred to the back surface of the paper, based on the correspondence between the image data of the front surface and the back surface when forming a double-sided image for forming images on the front and back sides of the paper. An image forming apparatus that performs control so that a transfer auxiliary agent is transferred to a region directly behind. The control means includes
The image forming apparatus according to claim 1, wherein the transfer auxiliary agent is transferred to a region on the surface of the paper where the toner image is not transferred. The control means includes
The image forming apparatus according to claim 1, wherein the transfer auxiliary agent is transferred to a region where a transfer amount of the toner image on the surface of the sheet is small. An image carrier on which an electrostatic latent image is formed based on image data;
A plurality of developing devices for developing the electrostatic latent image with toner or a transfer aid;
A transfer unit for transferring the developed toner image and transfer auxiliary agent to the paper;
A fixing unit for heating the paper on which the toner image and the transfer auxiliary agent are transferred;
A double-sided conveyance unit that conveys the heated paper in the fixing unit, reverses the paper, and then conveys the paper again to the transfer unit;
Control means;
An image forming apparatus having
The image forming apparatus according to claim 1, wherein the control unit controls the transfer auxiliary agent to be transferred to the entire area of the surface of the paper when the double-sided image is formed on the front and back of the paper. The image forming apparatus according to claim 1, wherein the transfer auxiliary agent is transparent fine particles or transparent toner. The image forming apparatus according to claim 1, wherein the transfer auxiliary agent is a carrier in which a magnetic carrier core is coated with a resin. The transfer aid transferred to the surface of the paper is not fixed to the paper by heating at the fixing unit,
A collecting means for collecting a transfer auxiliary agent remaining on the surface of the paper that has passed through the fixing unit;
The image forming apparatus according to claim 6, wherein the transfer auxiliary agent collected by the collecting unit is reusable by a developing device that develops the transfer auxiliary agent.

Images