JP2010204521A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus of high productivity, long service life, energy saving as well as with easy discrimination of the front and back surface even when back paper is used. <P>SOLUTION: A color printer 10 as the image forming apparatus is provided with: image forming sections 20 for respective colors forming toner images on an intermediate transfer belt 12; a secondary transfer section 16 for transferring the formed toner image to a first surface of the printing paper; and a fixing section 17 for fixing the image to the printing paper on which the toner image is transferred. In this case, a control section 35 is provided for carrying out control to prevent attaching of soiling to a second surface of the printing paper by at least one of the secondary transfer section 16 and a member (press roller 17a) that faces a second surface of the printing paper in the fixing section 17. In addition, the control section 35 does not carry out this control when printing to the back paper and carries out this control when not printing to the back paper according to whether or not the printing which is instructed to be executed is printing to the back paper. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, and a FAX.

  In recent years, in offices and the like, in order to reduce the amount of paper used, the back side (so-called back paper) of paper once printed on one side is used as printing paper. In such a printed matter, for example, if the contents are the same on the front and back, or if a large number of printed matter is scattered, it may be difficult to know which side is the latest print. there were. On the other hand, for example, Patent Document 1 proposes an apparatus that, when printing on a backing paper, forms an image with a mark that clearly indicates that the back side is reverse by using a reversing device after the image is formed. Has been. For example, Patent Document 2 proposes an apparatus that stamps a back surface before or after image formation.

JP-A-7-199738 JP-A-10-339974

  However, the conventional techniques described above have the following problems. For example, in the technique described in Patent Document 1, since the mark is printed by inverting the paper, the productivity is greatly reduced. In addition, there is a problem in that consumables are consumed and the life of the parts is shortened. Alternatively, in a device that pushes a stamp on the back surface, it is necessary to newly add a stamp device as a dedicated portion for that purpose. For this reason, there were problems of increased cost and increased space. Furthermore, there was a problem that stamp ink was added to the consumables.

  The present invention has been made to solve the problems of the conventional image forming apparatus described above. That is, an object of the present invention is to provide an image forming apparatus that is highly productive, has a long service life, is resource-saving, and can easily distinguish between the front and back surfaces even when a backing paper is used.

  An image forming apparatus according to the present invention, which has been made for the purpose of solving this problem, has a toner image forming portion that has an image carrier and forms a toner image on the image carrier, and is opposed to the image carrier with a print sheet interposed therebetween. An image having a transfer portion for transferring the toner image formed by the toner image forming portion to the first surface of the printing paper, and a pair of fixing members for fixing the image on the printing paper on which the toner image is transferred by the transfer portion. A forming apparatus, wherein at least one of a transfer unit and a member of a pair of fixing members facing a second surface of a printing paper (hereinafter referred to as a pressurizing member) causes stain on the second surface of the printing paper. A back-stain prevention control unit that performs control to prevent adhesion is performed, and the back-stain prevention control unit performs printing on the back paper depending on whether the print instructed to execute is printing on the back paper. If this is not the case, control is not performed. And it performs the control.

  According to the image forming apparatus of the present invention, the toner image formed on the image carrier is transferred to the first surface of the printing paper by the transfer unit. Accordingly, in the transfer process, the transfer portion faces the second surface of the printing paper. Next, the toner image transferred to the printing paper is fixed by being sandwiched between a pair of fixing members. In this fixing step, the pressure member faces the second surface of the printing paper. Therefore, if dirt is attached to any surface of the transfer unit and the pressure member, the dirt may adhere to the second surface of the printing paper. Therefore, conventionally, these members have been cleaned to prevent adhesion of dirt to the second surface.

  In the present invention, there is provided a back dirt prevention control unit that performs control for preventing the adhesion of dirt on the second surface of the printing paper, and whether or not to perform the control depending on whether or not the printing paper is the backing paper. Select. That is, if the printing paper is the back paper, the control for preventing the adhesion of dirt on the second surface is not performed. As a result, dirt adheres to the second surface of the backing paper, so the front and back surfaces can be easily distinguished. The image forming apparatus of the present invention has high productivity because it is not necessary to reverse the printing paper. In addition, since no consumables or special members are required, it has a long life and resource saving. As a result, the image forming apparatus is highly productive, has a long service life and is resource-saving, and can easily distinguish between the front and back surfaces even when a backing paper is used.

  The image carrier referred to in the present invention is a member on which a toner image is formed, and includes a photosensitive member and an intermediate transfer member. The transfer unit is a member disposed on the second surface side of the printing paper when the toner image is transferred to the printing paper. For example, in a two-time transfer system having an intermediate transfer belt, the secondary transfer portion corresponds to this. Further, in the direct transfer system having no intermediate transfer belt, the direct transfer belt corresponds to this.

Furthermore, in the present invention, there is a transfer cleaning unit that contacts the transfer unit and cleans the surface thereof, and when the back dirt prevention control unit does not perform control to prevent the adhesion of dirt, the transfer cleaning unit is transferred to the transfer unit. When the control is performed so as to prevent the adhesion of dirt, the transfer cleaning unit is preferably brought into contact with the transfer unit.
In this way, it is easy to control whether or not contamination on the surface of the transfer portion is prevented from adhering to the second surface of the printing paper.

Further, the present invention has a fixing cleaning unit that contacts the pressure member to clean the surface thereof, and the back dirt prevention control unit adds the fixing cleaning unit when the control for preventing the adhesion of dirt is not performed. In the case where control is performed to separate the pressure member and prevent the adhesion of dirt, it is desirable to bring the fixing cleaning unit into contact with the pressure member.
In this way, it is easy to control whether or not to prevent dirt on the surface of the pressure member from adhering to the second surface of the printing paper.

Further, in the present invention, a cleaning roller that contacts and cleans the surface of the transfer unit or the pressure member, a scraping member that scrapes off dirt from the surface of the cleaning roller, and a dirt reservoir member that receives dirt falling from the scraping member When the control for preventing the adhesion of dirt is not performed, the control unit for preventing the dirt from being attached is placed close to the dirt storage member and the scraping member to prevent the adhesion of dirt. The dirt storage member and the scraping member may be separated from each other.
When the dirt accumulating member and the scraping member are brought close to each other, the dirt accumulated in the dirt accumulating member flows backward to the cleaning roller via the scraping member. Therefore, dirt is attached to the surface of the transfer part or the pressure member. Accordingly, dirt is attached to the second surface of the printing paper, so that the front and back surfaces can be easily distinguished.

Furthermore, in the present invention, the back stain prevention control unit sets the temperature of the pressure member to a temperature lower than the temperature at which the toner image on the second surface of the printing paper melts when performing control to prevent the adhesion of stains. When the control for preventing the adhesion of the pressure is not performed, the temperature of the pressure member may be set higher than that for the control for preventing the adhesion of the dirt.
If the temperature of the pressure member is, for example, equal to or higher than the temperature at which the toner image on the second surface is melted, if there is a toner image or toner stain on the second surface, it is melted. That is, if there is a toner image on the second surface of the printing paper, it is melted and the image is disturbed. Furthermore, if the melted toner and the second surface of the printing paper come into contact with each other, dirt adheres to the second surface of the printing paper. Therefore, even if it does in this way, it will not prevent that the dirt adheres to the 2nd side of printing paper.

Furthermore, in the present invention, the presence or absence of an image on the second side of the printing paper used for image formation is detected, and when it is detected that there is an image, it is determined that the printing is on the back paper, and the absence of the image is detected. In this case, it is desirable to have a backing paper determination unit that determines that printing is not performed on the backing paper.
In this way, it is easy to determine whether or not the printing paper is a backing paper, and it is easy to use because it does not require user input or the like.

Furthermore, the present invention has a plurality of paper feeding units that feed printing paper toward the transfer unit, and printing on the back paper is performed when paper is fed from a predetermined one of the paper feeding units. It is desirable to have a back paper determination unit that determines that there is, and does not print on the back paper when paper is supplied from other paper supply units.
In many cases, a paper feeding unit for feeding the backing paper is determined in advance. Therefore, if it is determined that the paper is the back paper in the case of paper feeding from the paper feeding unit, the use is simple.

  According to the image forming apparatus of the present invention, the productivity is high, the life is long, the resources are saved, and the front and back surfaces can be easily distinguished even when the back paper is used.

1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment. It is explanatory drawing which shows a mode that a secondary transfer cleaner and a fixing | fixed part cleaner contact / separate. It is explanatory drawing which shows a back paper sensor. It is explanatory drawing which shows another mechanism of the state which prevents back stain | pollution | contamination. It is explanatory drawing which shows another mechanism for making it the state which does not prevent back dirt. It is explanatory drawing which shows another mechanism of the state which prevents back stain | pollution | contamination. It is explanatory drawing which shows another mechanism for making it the state which does not prevent back dirt. It is explanatory drawing which shows the state which does not prevent back dirt. It is a schematic block diagram which shows the image forming apparatus which concerns on a 2nd form.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a tandem color printer.

(First form)
The color printer 10 of the first embodiment is a so-called tandem type image forming apparatus capable of forming a color image, as shown in FIG. In the middle of the figure, four color image forming portions are arranged along the intermediate transfer belt 12 in the order of yellow 20Y, magenta 20M, cyan 20C, and black 20K from left to right in the figure. Four toner storage portions 11 (11Y, 11M, 11C, and 11K) that store toner of each color are provided above the intermediate transfer belt 12 in the drawing. That is, this embodiment is an intermediate transfer type image forming apparatus that once transfers the toner image formed by the image forming unit of each color to the intermediate transfer belt 12 and further transfers the toner image from the intermediate transfer belt to the printing paper.

  In addition, a plurality of detachable paper feed cassettes 13 are mounted at the bottom of the color printer 10 in FIG. Further, on the right side in the figure, a paper transport path 14 is provided from the bottom upward. A paper feed roller 15, a secondary transfer unit 16, a fixing unit 17, and a paper discharge roller 18 are provided in order from the bottom along the paper conveyance path 14. A discharge tray 19 is provided on the upper surface of the color printer 10.

  Each color image forming unit 20Y, 20M, 20C, 20K has a charging unit 22, a developing unit 24, a primary transfer unit 25, and a cleaner 26 in the clockwise direction in FIG. ing. Further, an exposure unit 23 is provided below the image forming unit for each color. The exposure unit 23 is common to each color. In addition, a portion of each photoconductor 21 exposed by the exposure unit 23 is between the charging unit 22 and the developing unit 24. In the drawing, only the yellow image forming unit 20Y is provided with a reference numeral, but the other colors have the same configuration.

  Further, in this embodiment, a secondary transfer cleaner 31 is provided at the lower right of the secondary transfer unit 16 in the drawing. The fixing unit 17 includes a pressure roller 17a, and a fixing unit cleaner 32 is provided at the lower right of the pressure roller 17a in the drawing. Each of the secondary transfer cleaner 31 and the fixing unit cleaner 32 is for contacting the respective cleaning objects and cleaning the surface thereof. Furthermore, each can be brought into and out of contact with the object to be cleaned. In addition, the color printer 10 of this embodiment includes a control unit 35 that controls each part of the apparatus, including position control of the secondary transfer cleaner 31 and the fixing unit cleaner 32.

  Next, the operation of each part when a color image is formed by the color printer 10 will be briefly described. At the time of image formation, the intermediate transfer belt 12 and the photosensitive members 21 of the respective colors are rotated as indicated by arrows in FIG. The photoreceptor 21 is uniformly charged by the charging unit 22 and subsequently exposed by the exposure unit 23. As a result, an electrostatic latent image based on the image data is formed on the surface of the photoreceptor 21. Next, toner is supplied to the electrostatic latent image by the developing unit 24, and a toner image is formed on the photoreceptor 21. The toner images of the respective colors are transferred onto the intermediate transfer belt 11 by the primary transfer unit 25 and superimposed. The toner remaining on the photosensitive member 21 after passing through the primary transfer area is scraped off by the cleaner 26.

  On the other hand, the sheets stored in the sheet feeding cassette 13 are pulled out one by one by the sheet feeding roller 15. Then, the toner image superimposed on the intermediate transfer belt 12 is transferred by the secondary transfer unit 16 to the paper conveyed through the paper conveyance path 14. The sheet on which the toner image is transferred is further conveyed upward and reaches the fixing unit 17. In the fixing unit 17, the toner is fixed to the sheet by being heated and pressurized. As a result, the paper on which the image has been formed is discharged to the paper discharge tray 19 by the paper discharge roller 18.

  Further, the secondary transfer section 16 is cleaned by the secondary transfer cleaner 31. The pressure roller 17 a is cleaned by the fixing unit cleaner 32. As shown in FIG. 2, the left side of the sheet conveyed in the sheet conveyance path 14 is a printing surface (first surface) on which the toner image is transferred by the secondary transfer unit 16. The secondary transfer unit 16 and the pressure roller 17a are arranged on the right side of the sheet conveyance path 14 in the drawing, and are in contact with the back surface (second surface) side with respect to the printing surface of the sheet. If these members come into contact with the paper with dirt such as toner attached thereto, the back surface of the printing paper may be stained.

  In order to prevent stains on the back side of the printing paper, the secondary transfer cleaner 31 normally contacts the secondary transfer unit 16 and cleans the surface during the secondary transfer process. During the fixing process, the fixing unit cleaner 32 comes into contact with the pressure roller 17a to clean the surface thereof. That is, the secondary transfer cleaner 31 and the fixing unit cleaner 32 prevent dirt from adhering to the back surface of the paper.

  In this embodiment, as shown in FIG. 2, the secondary transfer cleaner 31 and the fixing unit cleaner 32 can be brought into contact with and separated from each object to be cleaned. That is, under the control of the control unit 35, it can be moved up and down as indicated by arrows in the figure. In any of the lower positions indicated by the solid lines in the figure (a state separated from the object), the object cannot be cleaned. In this case, the secondary transfer unit 16 and the pressure roller 17a are not cleaned, so that even if the surface is dirty, the sheet directly faces the sheet. Therefore, this arrangement is an arrangement that does not prevent dirt from adhering to the back side of the paper.

  In this embodiment, when the control unit 35 determines that the printing is performed on the back paper, the control unit 35 does not prevent the adhesion of dirt on the back surface of the paper. For this purpose, the secondary transfer cleaner 31 and the fixing unit cleaner 32 are moved to the lower position and separated from the respective members to be cleaned. Both may be separated or only one of them. Since the back side when printing on the back paper is an unnecessary print side, the image quality on the front side is not affected. Also, this surface is soiled, suggesting that the surface is the back surface. That is, it becomes easy to distinguish the front and back surfaces. In addition, it is not necessary to perform the back dirt over the entire surface, and it may be enough to draw a horizontal line. Further, when the next printing paper is a new paper, the cleaner is brought into contact with the target member again at an appropriate timing so as not to affect the printing paper.

  Note that it is preferable to determine whether to prevent the adhesion of dirt on the back surface of the paper by selecting the paper feed cassette 13 or inputting an instruction by the user. For example, one of the plurality of paper feed cassettes 13 is set in advance for backing paper. Then, when the paper feeding from the paper feeding cassette 13 set for the back paper is started, it is only necessary to prevent the dirt from adhering to the back surface of the paper. Alternatively, the user may be able to input an instruction as to whether or not to use the backing paper by using a setting input key or the like provided on the outer surface of the apparatus. In any case, when one job is completed, it is preferable to prevent dirt from adhering to the back side of the paper again.

  Alternatively, as shown in FIG. 3, an image sensor 41 that detects the back side of the paper may be disposed in the paper conveyance path 14. If the image sensor 41 detects an image on the back side of the paper, it is determined that the paper is a back paper. In this way, there is no need to determine in advance the paper feed cassette 13 that uses the backing paper. In addition, since there is no need to give instructions every time when printing, the user's trouble is saved.

  Next, another embodiment of the fixing unit cleaner 43 is shown in FIG. The fixing unit cleaner 43 includes a suction roller 45, a brush 46, and a dirt reservoir 47. The suction roller 45 rotates in contact with the pressure roller 17a and sucks dirt on the surface of the pressure roller 17a. The brush 46 rotates to bring the tip of the bristle into contact with the suction roller 45 to scrape off dirt from the suction roller 45. Further, the dirt reservoir 47 is for receiving and accumulating dirt scraped off by the brush 46. Normally, the dirt reservoir 47 is disposed at a position slightly separated from the brush 46 so that the brush bristles of the brush 46 and the dirt accumulated in the dirt reservoir 47 do not come into contact with each other.

  In the case where the adhesion of dirt on the back surface of the paper is not prevented, instead of separating the fixing unit cleaner 32 from the pressure roller 17a, the dirt reservoir 47 is raised as shown in FIG. The dirt reservoir 47 is brought into contact. In this way, the dirt in the dirt reservoir 47 adheres to the brush 46 and the dirt on the brush 46 is increased. Then, dirt is attached to the pressure roller 17 a via the suction roller 45. Therefore, even in this case, dirt is attached to the back surface of the paper. A similar mechanism can be applied to the secondary transfer cleaner 31. In that case, the pressure roller 17a in the figure may be read as the secondary transfer unit 16.

  Furthermore, another type of fixing unit cleaner 32 is shown in FIG. The fixing unit cleaner 32 includes a rubber blade 51, a cleaner case 52, and a conveyance roller 53. The fixing unit cleaner 32 is disposed above the pressure roller 17a. The rubber blade 51 contacts the surface of the pressure roller 17a and scrapes off dirt such as toner. The lower part of the cleaner case 52 in the figure has an opening 52a. Then, the dirt scraped off by the rubber blade 51 is carried and stored in the cleaner case 52 from the opening 52a by the transport roller 53.

  In this embodiment, as shown in FIG. 6, the fixing unit cleaner 32 is arranged on the upper portion of the pressure roller 17a and is movable in the vertical direction in the figure. Usually, the fixing unit cleaner 32 is in contact with the surface of the pressure roller 17a. Therefore, the opening 52a is blocked by the surface of the pressure roller 17a. If it is determined that the printing is performed on the backing paper, as shown in FIG. 7, it is moved away from the surface of the pressure roller 17a and slightly upward. In such an arrangement, the opening 52a is not blocked. Therefore, the dirt accumulated in the cleaner case 52 flows out from the opening 52a and adheres to the surface of the pressure roller 17a. Thereby, it will be in the state which does not prevent the adhesion of the stain | pollution | contamination to the back surface of a paper. A similar mechanism can be applied to the secondary transfer cleaner 31. In that case, the pressure roller 17a in the figure may be read as the secondary transfer unit 16.

  In the case where the temperature of the pressure roller 17a is controlled, the temperature control may be stopped. Some image forming apparatuses perform temperature control so that the temperature of the pressure roller 17a during the fixing process does not become too high. This is because if the pressure roller 17a is as high as the fixing temperature, the image on the back surface may melt and adhere to the pressure roller 17a.

  Therefore, in this embodiment, this temperature control is stopped so that the pressure roller 17a is raised to a fixing temperature. For example, the pressure roller 17a may have a heat source separately from the heating side. Alternatively, in the case where a heat source dedicated to the pressure roller 17a is not provided and the temperature rise due to heating on the heating side is controlled by radiating heat, the degree of heat radiation may be lowered. In this way, as shown in FIG. 8, the image on the back surface melts and adheres to the pressure roller 17a. The same effect as preventing the adhesion of dirt on the back surface of the paper can be obtained by fusing and disturbing the image on the back surface, and attaching the image attached to the pressure roller 17a to the back surface of the paper again. .

  In the present embodiment, any one of the various configurations described above is used as a configuration in which the control unit 35 performs control to prevent dirt from adhering to the second surface of the printing paper or not. Also good. The process may be performed for either the secondary transfer unit 16 or the fixing unit 17 or both. Furthermore, even when performing both, the combination of each structure is arbitrary.

  As described above in detail, according to the color printer 10 of the present embodiment, when it is determined that the printing is performed on the backing paper, whether or not the printing is performed on the backing paper, the control unit 35. Thus, control is performed so as not to prevent adhesion of dirt on the back surface of the paper. Therefore, since the back side of the back paper is soiled, the front and back sides can be easily distinguished. In this way, it is not necessary to reverse the paper, so productivity is high. In addition, no consumer materials are consumed to distinguish the front and back surfaces. As a result, the image forming apparatus is highly productive, has a long service life and is resource-saving, and easily distinguishes between the front and back surfaces when a backing paper is used.

(Second form)
Next, a second embodiment embodying the present invention will be described. The color printer 60 of this embodiment is a direct transfer type image forming apparatus having a direct transfer belt 61 as shown in FIG. About the same member as the 1st form, the same numerals are attached and explanation is omitted.

  In the color printer 60 of this embodiment, the image forming units 20Y, 20M, 20C, and 20K for the respective colors are arranged along the direct transfer belt 61 in the vertical direction in FIG. Further, the direct transfer belt 61 is stretched between two rollers 62 and 63. During image formation, the image is rotated clockwise as indicated by an arrow in the figure. In the vicinity of the lower roller 63 in the figure, a direct transfer cleaner 65 is disposed so as to be able to contact and separate from the direct transfer belt 61. The direct transfer cleaner 65 is for cleaning the surface of the direct transfer belt 61.

  In this embodiment, at the time of image formation, the sheet is directly conveyed from the bottom upward through the space between the transfer belt 61 and each color photoconductor 21. Then, the toner images formed on the respective photoreceptors 21 of the image forming units 20Y, 20M, 20C, and 20K for the respective colors are directly transferred onto the conveyed paper. The sheet on which the transfer of the toner image from all the photosensitive members 21 has been completed is conveyed further upward as shown in FIG. The toner image on the paper is fixed by the fixing unit 17.

  Therefore, in the color printer 60 of this embodiment, the back surface of the paper directly contacts the surface of the transfer belt 61 when the printing surface of the paper faces the image forming units 20Y, 20M, 20C, and 20K of the respective colors. For this reason, if the surface of the direct transfer belt 61 is soiled, the back surface of the paper may be soiled. That is, in this embodiment, whether or not to prevent the adhesion of the stain to the back surface of the paper is controlled by controlling the contact and separation of the transfer cleaner 65 directly by the control unit 35.

  Therefore, when the control unit 35 determines that the paper to be used for image formation is the back paper, the control unit 35 separates the direct transfer cleaner 65 from the direct transfer belt 61. As a result, the back surface of the sheet comes into contact with the direct transfer belt 61 with the dirt adhered thereto, so that the dirt on the direct transfer belt 61 is not prevented. Accordingly, since the back side of the paper is dirty, it is easy to distinguish between the front and the back. In this embodiment, the direct transfer belt 61 corresponds to a part of the transfer portion.

  Furthermore, in this embodiment, various variations are conceivable as in the first embodiment. Further, similarly to the first embodiment, it is possible to control whether or not to prevent dirt from adhering to the second surface of the printing paper by the fixing unit 17. Either one of the direct transfer belt 61 and the fixing unit 17 may be performed, or both may be performed. Furthermore, even when performing both, the combination of each structure is arbitrary.

  As described above in detail, the color printer 60 according to the present embodiment also has an image forming apparatus that is highly productive, has a long life, saves resources, and easily distinguishes between the front and back surfaces when using a back paper. can do.

In addition, each said form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, the illustrated color printer is one example, and it is needless to say that the present invention is not limited to this and can be applied to a copying machine, a FAX machine, and the like. The configuration of the image forming unit and the fixing unit is not limited to this. Further, in the image forming apparatus further including the manual feed tray, the manual feed tray can be used for the backing paper.

10, 60 Color printer 13 Paper cassette 16 Secondary transfer unit 17 Fixing unit 17a Pressure roller 31 Secondary transfer cleaner 32, 43 Fixing unit cleaner 35 Control unit 41 Image sensor 45 Suction roller 46 Brush 47 Dirt reservoir 65 Direct transfer cleaner

Claims (8)

A toner image forming unit having an image carrier and forming a toner image on the image carrier; and a toner image formed by the toner image forming unit facing the image carrier with the print paper sandwiched therebetween. An image forming apparatus having a transfer portion to be transferred to the first surface of the image forming apparatus and a pair of fixing members for fixing the image on the printing paper on which the toner image has been transferred by the transfer portion.
Prevents contamination from adhering to the second surface of the printing paper by at least one of the transfer portion and a member of the pair of fixing members facing the second surface of the printing paper (hereinafter referred to as a pressure member). It has a back dirt prevention control unit that performs control,
The back-stain prevention control unit does not perform the control when the execution-instructed printing is printing on the back paper, and does not perform printing on the back paper. In this case, the image forming apparatus performs the control. The image forming apparatus according to claim 1,
A transfer cleaning unit that contacts the transfer unit and cleans its surface;
The back dirt prevention control unit
When control for preventing the adhesion of dirt is not performed, the transfer cleaning unit is separated from the transfer unit,
An image forming apparatus, wherein the transfer cleaning unit is brought into contact with the transfer unit when the control for preventing the adhesion of dirt is performed. The image forming apparatus according to claim 1, wherein:
A fixing cleaning unit that contacts the pressure member and cleans the surface thereof;
The back dirt prevention control unit
When the control for preventing the adhesion of dirt is not performed, the fixing cleaning unit is separated from the pressure member,
An image forming apparatus, wherein the fixing cleaning unit is brought into contact with the pressure member when control for preventing the adhesion of dirt is performed. The image forming apparatus according to claim 1, wherein:
A cleaning roller for cleaning the surface in contact with the transfer portion;
A scraping member for scraping off dirt from the surface of the cleaning roller;
A dirt reservoir member that receives dirt falling from the scraping member;
The back dirt prevention control unit
When the control for preventing the adhesion of dirt is not performed, the dirt reservoir member and the scraping member are brought close to each other,
An image forming apparatus, wherein when performing control to prevent the adhesion of dirt, the dirt reservoir member and the scraping member are separated from each other. The image forming apparatus according to claim 1, wherein:
A cleaning roller that contacts the pressure member and cleans its surface;
A scraping member for scraping off dirt from the surface of the cleaning roller;
A dirt reservoir member for receiving dirt falling from the scraping member;
The back dirt prevention control unit
When the control for preventing the adhesion of dirt is not performed, the dirt reservoir member and the scraping member are brought close to each other,
An image forming apparatus, wherein when performing control to prevent the adhesion of dirt, the dirt reservoir member and the scraping member are separated from each other. In the image forming apparatus according to any one of claims 1 to 5,
The back dirt prevention control unit
When performing control to prevent the adhesion of dirt, the temperature of the pressure member is set to a temperature lower than the temperature at which the toner image on the second surface of the printing paper is melted,
2. An image forming apparatus according to claim 1, wherein when the control for preventing the adhesion of dirt is not performed, the temperature of the pressure member is set higher than that for the control for preventing the adhesion of dirt. In the image forming apparatus according to any one of claims 1 to 6,
The presence or absence of an image on the second side of the printing paper used for image formation is detected, and if it is detected that there is an image, it is determined that printing is on the back paper, and if no image is detected, the back paper An image forming apparatus comprising a backing paper determination unit that determines that printing is not performed on a paper. In the image forming apparatus according to any one of claims 1 to 7,
A plurality of paper feeding units for feeding printing paper toward the transfer unit;
When paper is fed from a predetermined one of the paper feed units, it is determined that printing is on the back paper, and when paper is fed from other paper feed units, An image forming apparatus comprising a backing paper determination unit that determines that printing is not performed.

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