JP5286695B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer or a copier that employs an intermediate transfer system.

  Conventionally, when a recording paper having a small basis weight is used in an image forming apparatus using an intermediate transfer belt, the recording paper is transferred to the intermediate transfer belt in the secondary transfer unit that transfers the toner image from the intermediate transfer belt to the recording paper. Sometimes stuck to the belt. Therefore, there is a problem that it is difficult to transport the recording paper to the fixing device after the secondary transfer.

On the other hand, a problem similar to this occurred in the fixing device. For example, a recording paper having a small basis weight may be wound around a roll of a fixing device due to viscosity due to melting of toner transferred to the recording paper. Conventionally, it has been proposed that this problem can be solved by transferring foamed toner or transparent toner to the surface of the recording paper on which the toner image is transferred (see, for example, Patent Document 1). That is, there is a difference in the thickness of the recording paper between the portion where the foamed toner or the transparent toner is transferred and the portion where the toner is not transferred, thereby preventing the roll from being wound around the roll.
JP 2006-215205 A

  However, even if this conventional technique is applied to recording paper with a small basis weight, it becomes difficult for the recording paper to stick to the intermediate transfer belt in the secondary transfer section and to transport the recording paper to the fixing device. Could not solve the problem. That is, the prior art described in Patent Document 1 is a technique for preventing the recording paper conveyed to the fixing device after the secondary transfer from being wound around the roll of the fixing device. This is effective only for recording paper conveyed without problems to the apparatus.

  Here, even if the conventional technique described in Patent Document 1 is adopted, the reason why the recording paper cannot be prevented from adhering to the secondary transfer portion is as follows. This is probably because there is a difference in sheet peeling at the transfer section. That is, in the fixing device, due to melting of the toner transferred to the recording paper, the viscosity of the toner increases and the toner is wound around the roll. In such a case, wrapping of the recording paper can be avoided by creating an air layer between the melted toner and the roll as in Patent Document 1.

  However, in the secondary transfer portion, the recording paper is greatly charged due to the influence of the transfer voltage, and is electrostatically attached to the intermediate transfer belt. The recording sheet after the secondary transfer is charged almost throughout the entire surface. For example, as described in Patent Document 1, an air layer is formed several mm inside (upstream in the transport direction) from the leading end of the recording sheet. Even if it is made, the recording paper does not easily peel off from the intermediate transfer belt.

  Therefore, in view of the above circumstances, the present invention provides an image forming apparatus capable of suppressing the recording medium from sticking to the intermediate transfer body in the secondary transfer portion where the toner image is transferred from the intermediate transfer body to the recording medium. Objective.

In order to achieve the above object, an image forming apparatus according to claim 1 of the present invention conveys a recording medium and an image forming unit that transfers a toner image based on input image data to an intermediate transfer member. A transfer unit that transfers the toner image transferred to the intermediate transfer member onto the recording medium transferred by the transfer unit; and a fixing unit that fixes the toner image transferred to the recording medium by the transfer unit. And the image forming unit includes an image forming unit that transfers transparent toner that becomes transparent after fixing by the fixing unit, and the image forming unit is the most distal portion in the conveyance direction of the recording medium, and該搬into a plurality of regions spaced in the direction perpendicular to the feeding direction, the transparent toner, at least from the leading edge portion, characterized that you transfer as a part thereof protrudes There.

  According to the first aspect of the present invention, since the transparent toner is transferred so that a part of the transparent toner protrudes from the leading edge of the recording medium in the conveyance direction, the electrostatic force of the leading edge of the recording medium is caused by the transparent toner. Can be reduced. Therefore, in the secondary transfer portion where the toner image is transferred from the intermediate transfer member to the recording medium, the most advanced portion of the recording medium is easily peeled off from the intermediate transfer member, and the recording medium is prevented from sticking to the intermediate transfer member. Can do. Note that the “most advanced portion” here refers to a portion of the surface of the recording medium in contact with the intermediate transfer member that is closest to the transport direction. That is, it refers to the most advanced region including the edge portion on the recording medium conveyance direction side.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect of the present invention, the image forming apparatus further includes an adjusting unit that adjusts a transfer number and a transfer position of the transparent toner according to the type of the recording medium. It is a feature.

According to the second aspect of the present invention, since the number and position of transfer of the transparent toner are adjusted according to the type of the recording medium, the transparent toner is always used with an appropriate transfer amount for the recording medium. Can do. Therefore, wasteful consumption of the transparent toner can be reduced. The “transfer amount” of the transparent toner mentioned here includes the mass per unit area of the transparent toner. In addition to the size of the recording medium, the “type” of the recording medium mentioned here includes the basis weight when the recording medium is used as recording paper, the type of paper such as so-called plain paper, coated paper, and the like. .

  As described above, according to the present invention, there is provided an image forming apparatus capable of suppressing the recording medium from adhering to the intermediate transfer body in the secondary transfer portion where the toner image is transferred from the intermediate transfer body to the recording medium. Can do.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below in detail based on examples shown in the drawings. The recording medium is recording paper P, and the transparent toner is called clear toner. Further, portions common to the respective colors will be described by adding alphabetic characters indicating the respective colors after the reference numerals. FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to the present embodiment, and FIG. 2 is a schematic plan view schematically illustrating a transfer position of a clear toner with respect to a recording sheet. 3 is a schematic side view showing the state of the recording paper conveyed to the secondary transfer unit, and FIG. 4 is a schematic diagram schematically showing the state of the most advanced portion of the recording paper conveyed to the secondary transfer unit. It is a side view.

  First, the configuration of the image forming apparatus 10 according to the present embodiment will be briefly described. As shown in FIG. 1, the image forming apparatus 10 transfers a toner image of each color based on input image data to an endless belt-like intermediate transfer belt 24 described later, and forms a full color image. The image forming unit 12 of the type is included.

  The image forming unit 12 outputs an image of each color of clear (L), yellow (Y), magenta (M), cyan (C), and black (K) in order from the upstream side in the conveyance direction of the recording paper P. Image forming units 14L, 14Y, 14M, 14C, and 14K. The image forming units 14L to 14K are separated from each other by a predetermined distance along the moving direction of the intermediate transfer belt 24 (indicated by an arrow B). Side by side.

  Each of the image forming units 14L to 14K has photosensitive drums 16L to 16K as image carriers, and the photosensitive drums 16L to 16K are provided on the surface (peripheral surface) of a conductive metal cylinder. A photosensitive layer made of an organic photoconductor or the like is laminated, and is driven to rotate in a direction indicated by an arrow A (clockwise direction) at a predetermined process speed.

  This photosensitive layer is a function-separated type in which a charge generation layer and a charge transport layer are sequentially laminated, and usually has a high resistance. However, when irradiated with a laser beam, the specific resistance of the portion irradiated with the laser beam is reduced. It has a changing nature. In addition, the diameter of each of the photosensitive drums 16L to 16K is preferably in the range of 20 mm to 100 mm.

  Around each of the photosensitive drums 16L to 16K, chargers 18L to 18K as charging devices that uniformly charge the surface (circumferential surface) of the photosensitive drum 16 to a predetermined potential in order from the upstream side in the rotation direction. The surface (circumferential surface) of the uniformly charged photosensitive drums 16L to 16K is irradiated with a laser beam (image light) based on color-separated image data (image signal), and an electrostatic latent image is formed by exposure. Exposure devices 20L to 20K to be transferred, developing devices 22L to 22K for transferring (developing) charged toner (developer) to an electrostatic latent image to form a toner image, and a path in contact with the photosensitive drums 16L to 16K An endless belt-like intermediate transfer belt 24 stretched around the belt, primary transfer rolls 26L to 26K for transferring the toner images formed on the photosensitive drums 16L to 16K to the intermediate transfer belt 24, and primary transfer. And a cleaning device 28L~28K for removing transfer residual toner remaining on the surface of the photosensitive drum 16L～16K, is arranged after.

  The cleaning devices 28L to 28K are pressed against the surfaces (circumferential surfaces) of the photosensitive drums 16L to 16K, and are driven to rotate in a direction opposite to the rotation direction (arrow A direction) of the photosensitive drums 16L to 16K. Brush rolls 29L to 29K for scraping off transfer residual toner from the drums 16L to 16K are provided.

  Further, the primary transfer rolls 26L to 26K are disposed inside the intermediate transfer belt 24, and are provided at positions facing the photosensitive drums 16L to 16K, respectively. A contact portion between the photosensitive drums 16L to 16K and the intermediate transfer belt 24 by the primary transfer rolls 26L to 26K is a primary transfer portion (primary transfer position) T1.

  Further, a bias power source (not shown) for applying a primary transfer bias is connected to each of the primary transfer rolls 26L to 26K. Further, each bias power source is controlled by a control unit 30 as a control means, and the primary transfer bias applied to each primary transfer roll 26L to 26K can be changed. The illustrated chargers 18L to 18K are roll-shaped contact chargers, but non-contact chargers such as a scorotron and a solid discharge device can also be used.

  On the other hand, an intermediate transfer belt 24 as an intermediate transfer member includes primary transfer rolls 26L to 26K, a drive roll 32 that is rotationally driven by a drive source (not shown), a tension roll 33 that adjusts the tension of the intermediate transfer belt 24, and a later-described. Is wound around a backup roll 34 and a follower roll 35 disposed at a secondary transfer portion (secondary transfer position) T2 that rotates and moves in the direction of arrow B in synchronization with the rotation of the photosensitive drum 16 ( ).

The intermediate transfer belt 24 has a surface resistivity of 10 by dispersing a material for imparting conductivity such as carbon or an ion conductive material in a resin material such as polyimide, polyamideimide, polycarbonate, or fluorine resin. It is formed by adjusting to about ¹⁰ Ω / □ to 10 ¹² Ω / □ (measurement voltage: 100 V).

  Further, a transfer for transferring the toner image on the intermediate transfer belt 24 onto a recording sheet P conveyed by a conveyance mechanism 42 as a conveyance means described later at a position facing the backup roll 34 with the intermediate transfer belt 24 interposed therebetween. A secondary transfer roll 36 as a means is provided. A first conveyance belt 50 (described later) is wound around the secondary transfer roll 36, and a contact portion between the secondary transfer roll 36 and the intermediate transfer belt 24 is subjected to secondary transfer via the first conveyance belt 50. Part (secondary transfer position) T2.

  The image forming apparatus 10 also includes a toner removing device 38 that removes residual toner remaining on the intermediate transfer belt 24 after the toner image is transferred onto the recording paper P by the secondary transfer roll 36, and a secondary transfer. And a fixing device 40 as fixing means for fixing the toner image transferred onto the recording paper P by the roll 36.

  The transport mechanism 42 includes a pickup roll 46 that transports the recording paper P stored in the paper tray 44 one by one, and a pair of transport rolls 47 provided in the transport path of the recording paper P (four in the drawing). A guide member 48 for supplying the recording paper P to the secondary transfer portion (secondary transfer position) T2, a first transport belt 50 wound around the secondary transfer roll 36 and the guide roll 52, A second conveyance belt 58 that is disposed on the downstream side of the conveyance path of the recording paper P with respect to the first conveyance belt 50 and is wound around the guide rolls 54 and 56, and a paper discharge tray (on the downstream side of the fixing device 40). (Not shown).

  By the transport mechanism 42, the recording paper P stored in the paper tray 44 is fed to a secondary transfer portion (second transfer section (first transport belt 50) and backup roll 34 facing each other with the intermediate transfer belt 24 sandwiched therebetween. It is conveyed to the secondary transfer position (T2), conveyed from the secondary transfer portion (secondary transfer position) T2 to the fixing device 40, and conveyed from the fixing device 40 to the paper discharge tray.

  The image forming apparatus 10 configured as described above operates as follows to form a full-color image. Since the image forming units 14L to 14K for the respective colors have substantially the same configuration, the operation of forming a yellow toner image by the image forming unit 14Y will be described here. Further, before transferring the yellow toner image to the intermediate transfer belt 24, the clear toner image has already been transferred to the intermediate transfer belt 24 by the image forming unit 14L.

  First, the surface of the photosensitive drum 16Y is uniformly charged to a potential of about -600V to -800V by the charger 18Y. The surface of the uniformly charged photoreceptor drum 16Y is irradiated with a laser beam by the exposure device 20Y in accordance with yellow image data sent from the control unit 30. That is, an electrostatic latent image of a yellow print pattern is formed on the photosensitive layer of the photosensitive drum 16Y.

  The electrostatic latent image is an image formed on the surface (photosensitive layer) of the photosensitive drum 16Y by charging. In the photosensitive layer, the specific resistance of the portion irradiated with the laser beam decreases, and the photosensitive drum 16Y. This is a so-called negative latent image formed by the fact that the charged charge flows on the surface of the film and the charge remaining in the portion not irradiated with the laser beam remains.

  Thus, the electrostatic latent image formed on the photosensitive drum 16Y is conveyed to a predetermined development position by the rotation of the photosensitive drum 16Y. At this development position, the electrostatic latent image on the photosensitive drum 16Y is converted into a visible image (toner image) by the developing device 22Y. In the developing device 22Y, for example, yellow toner having a volume average particle diameter of at least 3 μm to 6 μm including at least a yellow colorant and a binder resin is accommodated.

  The yellow toner is triboelectrically charged by being agitated inside the developing device 22Y, and has a charge of the same polarity (−) as the charge on the surface of the photosensitive drum 16Y. Therefore, when the surface of the photosensitive drum 16Y passes through the developing device 22Y, the yellow toner is electrostatically attached only to the latent image portion on the surface of the photosensitive drum 16Y, and the latent image becomes yellow toner. It is developed by. Thereafter, the photosensitive drum 16Y continues to rotate, and the toner image developed on the surface thereof is conveyed to the primary transfer portion (primary transfer position) T1.

  When the yellow toner image on the surface of the photoreceptor drum 16Y is conveyed to the primary transfer portion (primary transfer position) T1, a predetermined primary transfer bias is applied to the primary transfer roll 26Y, and the photoreceptor drum 16Y applies the primary transfer roll 26Y. The heading electrostatic force acts on the toner image, and the toner image on the surface of the photosensitive drum 16Y is transferred to the surface of the intermediate transfer belt 24. The primary transfer bias applied at this time is a polarity (+) opposite to the polarity (−) of the toner. For example, in the image forming unit 14Y, the control unit 30 performs constant current control to about +20 μA to +30 μA.

  The transfer residual toner on the surface of the photosensitive drum 16Y is cleaned by the cleaning device 28Y. The primary transfer bias applied to the primary transfer rolls 26L and 26M to 26K of the image forming units 14L and 14M to 14K is also controlled in the same manner as described above. In this way, the intermediate transfer belt 24 onto which the yellow toner image has been transferred by the image forming unit 14Y is sequentially conveyed to the remaining color image forming units 14M to 14K, and transferred so that the toner images of the respective colors are overlapped. Multiple transcription).

  The intermediate transfer belt 24 on which the toner images of all the colors have been multiplex-transferred through the image forming units 14L to 14K are circumferentially conveyed in the direction of the arrow B shown in the figure, and contact the inner surface (back surface) of the intermediate transfer belt 24. The secondary transfer portion (secondary transfer position) T2 configured by the backup roll 34 and the secondary transfer roll 36 (first transport belt 50) disposed on the image holding surface side of the intermediate transfer belt 24 is reached.

  On the other hand, the recording paper P is fed by the transport mechanism 42 between the secondary transfer roll 36 (first transport belt 50) and the intermediate transfer belt 24 at a predetermined timing, and a predetermined secondary transfer bias is applied to the secondary transfer. Applied to the roll 36. The secondary transfer bias applied at this time has a polarity (+) opposite to the polarity (−) of the toner, and an electrostatic force from the intermediate transfer belt 24 toward the recording paper P acts on the toner image, and the intermediate transfer belt 24. Is transferred onto the surface of the recording paper P.

  Further, the secondary transfer bias at this time is determined according to the resistance detected by a resistance detection means (not shown) for detecting the resistance of the secondary transfer portion (secondary transfer position) T2, and is controlled by a constant voltage. ing. Thereafter, the recording paper P is sent to the fixing device 40, the toner image is heated and pressurized, and the color-superposed (multi-transferred) toner image is melted and permanently fixed on the surface of the recording paper P. . Thus, the recording paper P on which the fixing of the full-color image is completed is carried out toward the paper discharge tray, and a series of full-color image forming operations is completed.

  In the image forming apparatus 10 as described above, as shown in FIG. 2, the clear toner Lt is used not only for image formation, but also partially protrudes from the leading edge 60 in the conveyance direction of the recording paper P. Transcribed. Here, the leading end portion 60 in the conveyance direction of the recording paper P means a portion closest to the conveyance direction on the surface of the recording paper P in contact with the intermediate transfer belt 24. That is, it indicates the most advanced region including the edge portion 62 on the recording paper P conveyance direction side. Accordingly, the clear toner Lt is transferred so as to reach the most advanced surface 64 from the most advanced portion 60 of the normal recording paper P (see FIG. 4).

  As described above, when the clear toner Lt is transferred from the leading edge 60 of the recording paper P to the leading edge 64 (including the edge portion 62), the electrostatic force at the leading edge 60 of the recording paper P is reduced. Therefore, in the secondary transfer portion (secondary transfer position) T2 where the toner image is transferred from the intermediate transfer belt 24 to the recording paper P, the foremost portion 60 of the recording paper P moves from the intermediate transfer belt 24. Occurrence of a problem that the recording paper P after the secondary transfer is easily peeled off and sticks to the intermediate transfer belt 24 can be suppressed.

  That is, as shown in FIG. 3, the toner image fed to the secondary transfer portion (secondary transfer position) T <b> 2 by the transport mechanism 42 and primarily transferred to the intermediate transfer belt 24 is transferred to the backup roll 34 and the secondary roll 34. The recording sheet P that has been secondarily transferred by the transfer roll 36 is conveyed to the fixing device 40 without being attached to the intermediate transfer belt 24.

  The clear toner Lt has a property of becoming transparent after being fixed on the recording paper P by the fixing device 40. Further, the image forming unit 14L for transferring the clear toner Lt may be configured to transfer only to the most distal portion 60 in the conveyance direction of the recording paper P. That is, the clear toner Lt may be used to be transferred so that a part of the clear toner Lt protrudes from at least the leading edge 60 in the conveyance direction of the recording paper P.

Here, an evaluation test of sticking suppression at the secondary transfer portion T2 when image formation is performed using A4 size recording paper P (plain paper) having different basis weights will be described. As a comparative example, as shown in FIG. 5, 1 cm × inside a predetermined distance W (for example, W = 1 cm) from the most distal portion 60 (edge portion 62) in the conveyance direction of the recording paper P (upstream in the conveyance direction). A clear toner Lt patch having a transfer size of 4 g / m ² with a size of 1 cm is changed by changing the transfer number (the transfer interval (transfer position) in the width direction perpendicular to the conveyance direction of the recording paper P). ) Three patterns were prepared for the transfer. That is, the number of transfer is 2 in FIG. 5A, 3 in FIG. 5B, and 5 in FIG. 5C.

  Then, in the secondary transfer portion T2 at the time of forming an image on the recording paper P of each pattern, the presence or absence of sticking to the intermediate transfer belt 24 is investigated, and the paper transportability in the secondary transfer portion T2 is evaluated as basis weight. This was carried out for each recording paper P having a different size. The results are shown in Table 1. For reference, Table 1 also shows the results when the recording paper P that does not transfer the clear toner Lt is used. As can be seen from the results in Table 1, when the clear toner Lt is not transferred to the recording paper P and when the clear toner Lt is transferred to the positions shown in FIGS. However, it was difficult to transport the recording paper P having a size of 60 gsm or less.

Next, the present embodiment in which the clear toner Lt is transferred to the leading edge 60 of the recording paper P will be described. As shown in FIG. 2, the recording paper P has a size of 1 cm × 1 cm so as to protrude from the most distal portion 60 (edge portion 62) in the conveyance direction by a predetermined distance D (for example, D = about 3 mm). A clear toner Lt patch with a transfer amount of 4 g / m ² transferred with the transfer number changed (the transfer interval (transfer position) changed in the width direction perpendicular to the conveyance direction of the recording paper P). Three patterns were prepared. That is, the number of transfer is 2 in FIG. 2A, 3 in FIG. 2B, and 5 in FIG. 2C.

  Then, in the secondary transfer portion T2 at the time of forming an image on the recording paper P of each pattern, the presence or absence of sticking to the intermediate transfer belt 24 is investigated, and the paper transportability in the secondary transfer portion T2 is evaluated as basis weight. This was carried out for each recording paper P having a different size. The results are shown in Table 2. The reason why the clear toner Lt is transferred from the leading edge 60 of the recording paper P by about 3 mm as the predetermined distance D is to form the clear toner Lt aiming at the leading edge 60 of the recording paper P. In particular, it is not limited to 3 mm. That is, the predetermined distance D may be 3 mm or more, or less than 3 mm.

  However, when the clear toner Lt is transferred to the edge of the leading edge 60 of the recording paper P (so as not to protrude from the leading edge 60), the recording is performed when the position of the recording paper P is shifted due to image misalignment or skew. In some cases, the clear toner Lt cannot be transferred to the leading edge 60 of the paper P. On the other hand, if the clear toner Lt is transferred so as to protrude too much, it becomes possible to transfer the clear toner Lt to the most advanced portion 60 of the recording paper P, but wasteful consumption of the clear toner Lt increases. It is not preferable. Therefore, it is desirable to transfer the clear toner Lt so that it protrudes from the most advanced portion 60 (edge portion 62) of the recording paper P by a predetermined distance D = about 3 mm in the transport direction.

  As shown in Table 2, in the evaluation result of this example, the recording paper P having a basis weight of 50 gsm could be conveyed without any problem. Further, the recording paper P having a basis weight of less than 50 gsm may or may not be effective depending on the transfer amount (transfer number and transfer position) of the clear toner Lt. In other words, it has been found that for the recording paper P having a basis weight of less than 50 gsm, the effect can be obtained by increasing the transfer number (transfer amount) of the clear toner Lt transferred to the most distal portion 60 in the transport direction. .

  This is due to the peeling shape of the recording paper P and the effect of the stiffness of the recording paper P, and the stiffness of the recording paper P becomes weaker as the basis weight becomes smaller. That is, in the recording paper P having a basis weight of less than 50 gsm, even if the peeling occurs in a part of the most advanced portion 60, the stiffness is weak, and therefore the peeling may occur only in a part of the area (only locally). On the other hand, in the recording paper P having a basis weight of 50 gsm or more, if peeling occurs at a part of the most advanced portion 60, the stiffness is strong and the remaining part is always peeled off.

  Therefore, in the recording paper P having a basis weight of 50 gsm or more, there may be few places (transfer number) to which the clear toner Lt is transferred, and on the contrary, in the recording paper P having a basis weight of less than 50 gsm, the place to which the clear toner Lt is transferred ( It is necessary to increase the number of transcriptions). In any case, once the leading edge 60 of the recording paper P is peeled off from the intermediate transfer belt 24, the remaining portion is continuously peeled off from the intermediate transfer belt 24 due to the effect of the stiffness of the recording paper P. Therefore, it is extremely effective to use a configuration in which the leading edge 60 of the recording paper P is peeled off from the intermediate transfer belt 24 by the clear toner Lt.

  Further, the transfer amount (including the transfer number and transfer position) of the clear toner Lt can be adjusted as appropriate by an adjustment unit 31 included in the control unit 30. That is, the memory (not shown) provided in the adjusting unit 31 stores in advance the type (for example, plain paper, coated paper, etc.), size (for example, A3, A4, B4, B5, etc.), basis weight of the recording paper P. For each (for example, 80 gsm, 70 gsm, 60 gsm, 50 gsm, etc.), an appropriate clear toner Lt transfer amount (including the transfer number and transfer position) is stored.

  Accordingly, when the operator inputs the type, size, basis weight, etc. of the recording paper P to be used (in the present invention, these are collectively referred to as “type”) from an operation panel (not shown), an appropriate clear is performed from the memory. The transfer amount (including the transfer number and transfer position) of the toner Lt is read, and the clear toner Lt is transferred to the recording paper P based on the read amount. Therefore, it is possible to reduce useless consumption of the clear toner Lt.

  The sticking phenomenon of the recording paper P to the intermediate transfer belt 24 after the secondary transfer in which the toner image is transferred from the intermediate transfer belt 24 to the recording paper P is also caused by the environment in which the image forming apparatus 10 is installed, particularly humidity. Affected. Therefore, the humidity may be added as a parameter (reference for determining the transfer amount) stored in the memory.

  Here, the operation of the adjusting unit 31 will be described in detail. First, the humidity is detected by a humidity detection device (not shown) built in the image forming apparatus 10. Then, the operator operates the operation panel to input the type of recording paper P. For example, input is A4 size coated paper having a basis weight of 43 gsm. Then, an appropriate transfer amount (including the transfer number and transfer position) of the clear toner Lt in this case is read from the memory of the adjusting unit 31.

That is, for example, when an A4 size coated paper having a basis weight of 43 gsm is used in a lateral feed in an environment with a humidity of 50%, the coated paper is easily charged, so the clear toner transferred to the most advanced portion 60 thereof. The transfer amount of Lt is 4.5 g / m ^{2 in} a size of 1 cm (transport direction) × 2 cm (direction orthogonal to the transport direction), the number of transfers is 8, and the transfer interval (transfer position) of each clear toner Lt is thereby Reads out as 2 cm.

  As a result, the transfer amount (including the transfer number and transfer position) of the clear toner Lt transferred to the leading edge 60 of the recording paper P (in this case, coated paper) is determined, and the intermediate transfer belt 24 is determined by the image forming unit 14L. The clear toner Lt is transferred to a predetermined position (a position where a part of the clear toner Lt protrudes from the foremost portion 60 when transferred from the intermediate transfer belt 24 to the recording paper P). Therefore, the clear toner Lt is transferred efficiently.

  As described above, since the image forming apparatus 10 according to the present embodiment is configured to transfer the clear toner Lt to the leading edge 60 of the recording paper P, the electrostatic force of the leading edge 60 of the recording paper P is reduced. Can be reduced. Therefore, even when the recording paper P having a small basis weight is used, the recording paper P after the secondary transfer can be prevented from sticking to the intermediate transfer belt 24. That is, the recording paper P after the secondary transfer can be conveyed to the fixing device 40 without being attached to the intermediate transfer belt 24.

Schematic configuration diagram showing an image forming apparatus according to the present embodiment Schematic plan view schematically showing the transfer position of the clear toner on the recording paper Schematic side view showing the state of the recording paper conveyed to the secondary transfer section Schematic side view schematically showing the state of the leading edge of the recording paper conveyed to the secondary transfer unit Schematic plan view schematically showing the transfer position of the clear toner on the recording paper of the comparative example

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image forming means 14 Image forming unit 16 Photosensitive drum 20 Exposure apparatus 22 Developing apparatus 24 Intermediate transfer belt (intermediate transfer body)
26 Primary transfer roll 28 Cleaning device 30 Control unit 31 Adjustment means 34 Backup roll 36 Secondary transfer roll (transfer means)
38 Toner removing device 40 Fixing device (fixing means)
42 Conveying mechanism (conveying means)
60 Cutting Edge Lt Clear Toner (Transparent Toner)
P Recording paper (recording medium)

Claims (2)

Image forming means for transferring a toner image based on input image data to an intermediate transfer member;
Conveying means for conveying the recording medium;
Transfer means for transferring the toner image transferred to the intermediate transfer member onto the recording medium conveyed by the conveyance means;
Fixing means for fixing the toner image transferred to the recording medium by the transfer means;
With
The image forming unit has an image forming unit that transfers transparent toner that becomes transparent after fixing by the fixing unit;
The image forming unit, said the conveying direction leading end of the recording medium, and a plurality of regions spaced in the direction perpendicular to the conveying direction, the transparent toner, from at least the most distal end portion, a part an image forming apparatus comprising that you transfer such that protrude. The image forming apparatus according to claim 1, further comprising an adjusting unit that adjusts a transfer number and a transfer position of the transparent toner according to a type of the recording medium.

Images