JP5464797B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that uses an electrophotographic recording system such as a laser printer, a copying machine, or a facsimile.

  In an image forming apparatus such as a copying machine, a printer, or a fax machine, an electrophotographic system using toner is often used. In these image forming apparatuses, there is a transfer process in which a toner image, which is a developer image carried on a photosensitive drum, which is an image carrier, is electrostatically transferred to a transfer material or an intermediate transfer belt surface.

  In the transfer process, transfer bias applying means for applying a necessary bias is provided to electrostatically transfer the toner. As a transfer means connected to a high-voltage power supply, the transfer roller or the like is in contact with the photosensitive drum across the recording material conveyance belt or intermediate transfer belt (on the back side of the recording material conveyance belt or intermediate transfer belt). A configuration in which a transfer member is arranged is often used.

  FIG. 18 is a sectional view of a configuration using a transfer roller as a transfer member. As shown in FIG. 18, an intermediate transfer belt 120, which is an endless belt-shaped intermediate transfer body, is in contact with the photosensitive drum 102a in a contact area N1. The transfer roller 145a for primary transfer is in contact with the intermediate transfer belt 120 in the contact area N2. Therefore, the transfer roller 145 a for primary transfer and each photosensitive drum 102 a form a nip via the intermediate transfer belt 120. A primary transfer power supply 140a is connected to the transfer roller 145a.

  The toner image formed on the photosensitive drum 102a is rotated by an intermediate transfer belt 120 rotated by a transfer roller 145a to which a primary transfer bias (a polarity opposite to that of toner (positive polarity)) is applied from a primary transfer power supply 140a. Primary transfer is performed on the top.

  In this configuration, when there is a contact start end on the upstream side in the rotation direction of the intermediate transfer belt 120 and the transfer roller 145a outside the contact area N1, the toner image on the photosensitive drum 102a is pre-transferred onto the intermediate transfer belt. End up. The pre-transfer is generated by a transfer electric field formed by a transfer bias applied to the transfer roller 145a, and the pre-transfer may cause a deterioration in image quality such as so-called scattering.

  Further, when there is a contact end point on the downstream side in the rotation direction between the intermediate transfer belt 120 and the transfer roller 145a in the contact area N1, peeling discharge is caused by a sudden change in potential at the peeling portion between the intermediate transfer belt 120 and the photosensitive drum 102a. May occur. The toner image on the intermediate transfer belt may be disturbed due to the peeling discharge. In order to suppress the stripping discharge, the configuration provided with the charge eliminating member leads to an increase in size and cost of the apparatus.

  Further, the contact width between the intermediate transfer belt 120 and the transfer roller 145a (so-called transfer nip width) may be uneven in the longitudinal direction due to the influence of the deflection of the transfer roller 145a. In this case, the current required for the transfer process becomes non-uniform in the longitudinal direction, and image defects such as transfer defects occur.

  On the other hand, a configuration using brush-like transfer means has been proposed. In the configuration using the transfer brush as the transfer means, each fiber constituting the brush is in contact with the transfer belt or the intermediate transfer belt independently. For this reason, the contact area with the transfer belt or the intermediate transfer belt can make the contact state in the longitudinal direction uniform, and transfer defects are suppressed (Patent Document 1).

  FIG. 19 is a structural cross-sectional view using a transfer brush as a transfer member. Members having the same functions as those in FIG. 18 are denoted by the same reference numerals, and redundant description is omitted. As shown in FIG. 19, the transfer brush 146 a for primary transfer is in contact with each photosensitive drum 102 a via the intermediate transfer belt 120. The toner image formed on the photosensitive drum 102a is primarily transferred onto the rotating intermediate transfer belt 120 by a transfer brush 146a to which a primary transfer bias is applied.

  In this configuration, since the contact start end on the upstream side of the intermediate transfer belt 120 and the transfer brush 146a is in the contact area N1, it is possible to suppress the pre-transfer of the toner image on the photosensitive drum 102a onto the intermediate transfer belt 120. . For this reason, it is possible to suppress a decrease in image quality such as so-called scattering.

  Further, since there is a contact end end on the downstream side of the intermediate transfer belt 120 and the transfer brush 146a outside the contact area N1, peeling discharge due to a sudden potential change does not occur at the peeling portion of the intermediate transfer belt 120 and the photosensitive drum 102a.

  However, when the transfer brush 146a is used for a long period of time, there is a problem that the tip of the transfer brush 146a is crushed and deformed.

  Specifically, by pressing the transfer brush 146a against the intermediate transfer belt 120, each fiber constituting the transfer brush 146a falls down. When used in such a state, the fibers of the transfer brush 146a may be deformed with wrinkles in a collapsed state.

  As a result, since the desired contact area between the intermediate transfer belt 120 and the transfer brush 146a is not formed, problems such as the above-described pre-transfer, peeling discharge, and transfer failure due to non-uniform contact width occur.

  As a transfer means, a method has been proposed in which a conductive sheet member (hereinafter referred to as a transfer sheet) having good slidability is brought into surface contact with a recording material conveyance belt or an intermediate transfer belt back surface and fixed at a predetermined position.

  For example, in a tandem color image forming apparatus, a conductive sheet member (transfer sheet) having good slidability is sandwiched and fixed between an elastic sheet member and a recording material conveyance belt. At this time, a member of the elastic sheet formed with different elasticity that increases the pressure from the center to both ends is used. In this configuration, a method for suppressing a transfer defect by applying a uniform transfer current has been proposed (Patent Document 2).

  FIG. 20 is a structural cross-sectional view using a transfer sheet as a transfer member. Members having the same functions as those in FIG. 18 are denoted by the same reference numerals, and redundant description is omitted. As shown in FIG. 20, the transfer sheet 147a for primary transfer is in contact with the recording material conveyance belt 135 in a state having the contact region N2, and is further in contact with and pressed against the elastic sheet 148a.

  The elastic sheet 148a is supported by the elastic sheet support member 149a.

  Accordingly, the elastic sheet 148a urges the recording material conveyance belt 135 through the transfer sheet 147a, and further urges each photosensitive drum 102a through the recording material P during image formation. A primary transfer power supply 140a is connected to the transfer sheet 147a. The toner image formed on the photosensitive drum 102a is superimposed and transferred onto the recording material P carried on the recording material conveyance belt 135 by the transfer sheet 147a to which the primary transfer bias is applied.

  Also in this configuration, the contact start end on the upstream side of the recording material conveyance belt 135 and the transfer sheet 147a is disposed in the contact region N1 (substantially the same as the contact region of the recording material P and the photosensitive drum 102a). Thereby, pre-transfer can be suppressed and so-called deterioration of image quality such as scattering can be suppressed.

  Further, the contact end of the recording material conveyance belt 135 and the transfer sheet 147a downstream is disposed outside the contact area N1. As a result, no peeling discharge due to a sudden potential change occurs at the peeling portion between the recording material P and the photosensitive drum 102a.

JP 05-127546 A Japanese Patent No. 3388535

  However, in the configuration of the conventional example as shown in Patent Document 2, a wave of the transfer sheet may occur when the use is continued. Due to the wave, the contact area N1 and the surface pressure of the transfer nip width become non-uniform and the transfer current value becomes non-uniform, resulting in a transfer failure.

  The above phenomenon occurs for the following two reasons.

1. Transfer sheet pasting accuracy If the transfer sheet 147a pasting accuracy is poor, a portion where the transfer sheet 147a is extended or contracted is generated. In particular, a wave is generated corresponding to the portion contracted in the longitudinal direction.

2. Transfer Sheet Elongation Due to Durability When the use is continued, the transfer sheet 147a receives an extension force in the longitudinal direction due to a belt offset force or the like. That is, the means for fixing the transfer sheet 147a fixes the upstream side in the rotation direction of the intermediate transfer belt 120 or the recording material conveyance belt, and does not fix the downstream side. In this case, on the upstream side, force acts in a direction to prevent the sheet from being stretched by the fixing means, whereas on the downstream side, no fixing means is provided. For this reason, force does not work in the direction to prevent the transfer sheet 147a from stretching. Accordingly, the transfer sheet extends so as to become longer toward the downstream side, resulting in a wave.

  The following three means are conceivable as means for preventing such transfer sheet waves.

1. 1. Increase the rigidity of the transfer sheet. 2. Affix the transfer sheet to the elastic sheet transfer surface side. Fix both upstream and downstream of the transfer sheet. However, it cannot be used for the following reasons.

  1. When the rigidity of the transfer sheet 147a is increased as described above, although there is an effect of preventing the elongation, the transfer sheet 147a cannot be arranged to follow the elastic sheet 148a cleanly. As a result, the transfer sheet 147a and the elastic sheet 148a may repel each other and protrude in front of the transfer sheet during use.

  Then, the toner image on the photosensitive drum may be pre-transferred onto the intermediate transfer belt 120 or the recording material due to the transfer electric field, which may cause a reduction in image quality such as so-called scattering.

  Further, since the transfer sheet 147a is hard, the intermediate transfer belt 120 or the recording material conveyance belt is scraped off particularly at the end of the transfer sheet 147a. If the scraped scrap enters the sensor facing roller for density detection or color misregistration detection, it becomes sensor signal noise. Further, when scraped scraps are mixed between the intermediate transfer belt 120 or the recording material conveying belt and the transfer sheet 147a, a transfer failure occurs.

  2. When the transfer sheet 147a is attached to the elastic sheet 148a as described above, although there is an effect of preventing elongation, the attaching accuracy becomes very severe. A convex portion is generated corresponding to a portion where the transfer sheet 147a is contracted and attached, the surface pressure of the contact area N1 and the transfer nip width becomes non-uniform, and the transfer current value becomes non-uniform. Transfer defects will occur.

  3. If both the upstream and downstream sides of the transfer sheet 147a are fixed as described above, there is a slight effect of preventing the elongation, but the portion between the upstream and downstream is not fixed, so the elongation will eventually occur, generating a wave I will let you. In addition, the fixing accuracy of the transfer sheet 147a is 2. , The contact area N1 and the surface pressure of the transfer nip width become non-uniform and the transfer current value becomes non-uniform, resulting in transfer failure.

  Note that the same phenomenon occurs in the case of an image forming apparatus using an intermediate transfer belt and also in the case of an image forming apparatus using a recording material conveyance belt that is directly superimposed and transferred onto a recording material.

  Therefore, the present invention provides an image forming apparatus capable of suppressing pre-transfer and peeling discharge from the initial use to the latter stage and obtaining a high-quality image without causing an increase in size and cost of the apparatus with a simple configuration. The purpose is to do.

In order to solve the above problems, a typical configuration of an image forming apparatus according to the present invention includes an image carrier that carries a toner image, and a rotatable endless belt that conveys the toner image transferred from the image carrier. includes a member, a transfer means for contacting to the back surface of the endless belt member corresponding to the contact surface between the image bearing member of the endless belt member, wherein the image carried by the transfer means to which a voltage is applied In an image forming apparatus in which a toner image is transferred from a body to the endless belt body side, the transfer unit is in contact with the back surface of the endless belt member and is pressed toward the endless belt member ; wherein the transfer sheet at the free end the other end one end of which is fixed, and the and the free end is disposed downstream in the rotation direction of the endless belt member, for holding one end of the transfer sheet holding Element And the holding member has a shape in which the center side of the holding member protrudes downstream in the rotational direction of the endless belt member from both ends with respect to the longitudinal direction orthogonal to the moving direction of the endless belt member, By supporting one end side of the transfer sheet by the holding member, the one end side of the transfer sheet is changed into a shape in which the center side protrudes downstream in the rotation direction of the endless belt member from both end sides. To do.

  According to the present invention, pre-transfer and peeling discharge can be suppressed from the initial stage of use to the latter stage without increasing the size and cost of the apparatus with a simple configuration, and a high-quality image can be obtained.

[First embodiment]
A first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings.

(1) Image Forming Apparatus FIG. 1 is a schematic configuration diagram showing a color image forming apparatus (electrophotographic intermediate transfer type full color printer) according to the present embodiment.

  As shown in FIG. 1, the color image forming apparatus includes four image forming units 1Y, 1M, 1C, and 1Bk that form yellow, magenta, cyan, and black images. The four image forming units 1 are arranged in a line at a constant interval.

  Each image forming unit 1 is provided with photosensitive drums 2a, 2b, 2c, and 2d as image carriers. Around each photosensitive drum 2, charging rollers 3a, 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer sheets (sheet-like transfer members, transfer means) 5a, 5b, 5c, 5d, drums Cleaning devices 6a, 6b, 6c and 6d are respectively installed. Exposure devices 7a, 7b, 7c, and 7d are installed above the charging roller (charging unit) 3 and the developing device (developing unit) 4, respectively. Each developing device 4 stores yellow toner, magenta toner, cyan toner, and black toner having negative charging characteristics.

  The photosensitive drum 2 is a negatively charged organic photosensitive member having a photosensitive layer on an aluminum drum base, and is rotated at a predetermined process speed in a direction indicated by an arrow (counterclockwise) by a driving device (not shown). The

  Each of the charging rollers 3 is in contact with the photosensitive drum 2 with a predetermined pressing force, and a desired charging bias is applied by a charging bias power source (not shown), so that the surface of each photosensitive drum 2 is uniformly set to a predetermined potential. Is charged. Each photosensitive drum 2 is negatively charged by each charging roller 3.

  The exposure device (laser scanner device) 7 outputs, from a laser output unit (not shown), laser light modulated in accordance with time-series electric digital pixel signals of image information respectively input from a host computer (not shown). . The output laser light exposes the surface of each photosensitive drum 2 through each reflecting mirror (not shown), and the surface of each photosensitive drum 2 charged by each charging roller 3 is electrostatically charged according to image information. A latent image is formed.

  The developing device 4 uses a contact developing method as a developing method, and has a developing roller as a developer carrier. The toner carried on a thin layer on the developing roller is conveyed to a portion (developing portion) facing the photosensitive drum 2 by a developing roller rotated by a developing driving means (not shown). The electrostatic latent image formed on the photosensitive drum is developed as a toner image (reverse development) by a developing bias applied to a developing roller by a developing voltage applying unit (not shown).

  Each developing roller and each photosensitive drum 2 in the developing device 4 are in contact in the full-color image forming mode, and in the mono-color image forming mode described later, the developing roller other than the developing unit that forms an image and the photosensitive drum 2 are separated from each other. It is the composition which does. This is to prevent deterioration and consumption of the developing roller and toner.

  The transfer sheet 5 for primary transfer is made of a sheet made of a resin such as nylon, EVA, PE or the like having conductivity.

  The intermediate transfer belt 20 is a rotatable intermediate transfer member (endless belt member). The intermediate transfer belt 20 is made of a resin such as PVdF (vinylidene fluoride resin), ETFE (tetrafluoroethylene-ethylene copolymer resin), polyimide, PET (polyethylene terephthalate), polycarbonate, or a rubber base layer such as EPDM. In addition, for example, urethane rubber coated with a fluorine resin such as PTFE is coated.

  The photosensitive drum 2 a is in contact with the surface (contact surface) of the intermediate transfer belt 20. The transfer sheet 5a is pressed in surface contact with the back surface (the surface opposite to the contact surface) of the intermediate transfer belt 20 by an elastic member (pressing member) 15a held by the transfer portion holding member 16a. As described above, the elastic member 15 a is urged to the respective photosensitive drums 2 a via the transfer sheet 5 a and the intermediate transfer belt 20 to form the primary transfer portion N. A primary transfer power supply 40a is connected to the transfer sheet 5a.

  The toner image developed on the photosensitive drum 2a is primarily transferred onto the rotating intermediate transfer belt 20 by a transfer sheet 5a to which a primary transfer bias is applied.

  The above is the transfer unit configuration of the image forming unit 1Y, and the other image forming units 1M, 1C, and 1Bk have the same configuration.

  The secondary transfer counter roller 23 is in contact with the secondary transfer roller 24 via the intermediate transfer belt 20 to form a secondary transfer portion M. The secondary transfer roller 24 is installed so as to be able to contact and separate from the intermediate transfer belt 20. A charging roller (ICL roller) 30 as a cleaning charging member (contact charging member) is in contact with the downstream side of the secondary transfer portion M of the intermediate transfer belt 20 in the rotation direction. The ICL roller 30 removes and collects the transfer residual toner remaining on the surface of the intermediate transfer belt 20. A cleaning power source (not shown) is connected to the ICL roller 30, and a belt cleaning device is configured by the ICL roller 30 and the cleaning power source.

  A fixing device 12 having a fixing roller 12a and a pressure roller 12b is installed downstream of the secondary transfer portion M in the conveyance direction of the recording material P.

(Image forming operation)
Next, an image forming operation by the color image forming apparatus will be described.

  When an image forming operation start signal is issued, each photosensitive drum 2 of the image forming unit 1 that is rotationally driven at a predetermined process speed is uniformly charged by the charging roller 3 to the negative polarity in this embodiment. Then, the exposure device 7 converts the input color-separated image signal into an optical signal by a laser output unit (not shown), and each photosensitive drum charged with the laser beam, which is the converted optical signal. 2 is scanned and exposed to form an electrostatic latent image.

  First, yellow toner is charged on the surface of the photoreceptor by the developing device 4a in which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied onto the photosensitive drum 2a on which the electrostatic latent image is formed. The electrostatic latent image is visualized by electrostatic attraction according to the electric potential to obtain a developed image. The yellow toner image is primarily transferred onto the rotating intermediate transfer belt 20 by the transfer sheet 5a to which a primary transfer bias (polarity opposite to the toner (positive polarity)) is applied in the primary transfer portion N. The The intermediate transfer belt 20 to which the yellow toner image is transferred is rotated toward the image forming unit 1M.

  In the image forming unit 1M, the magenta toner image formed on the photosensitive drum 2b in the same manner is superimposed on the yellow toner image on the intermediate transfer belt 20 and transferred by the primary transfer unit N. The

  In the same manner, yellow and black toner images formed on the photosensitive drums 2c and 2d of the image forming units 1C and 1Bk on the yellow and magenta toner images superimposed and transferred on the intermediate transfer belt 20 in the same manner are respectively primary. The images are sequentially overlapped at the transfer portion N. As a result, a full-color toner image is formed on the intermediate transfer belt 20.

  The recording material P is conveyed to the secondary transfer portion M by the feeding roller (registration roller) 13 in accordance with the timing when the front end of the full color toner image on the intermediate transfer belt 20 is moved to the secondary transfer portion M. Full-color toner images are secondarily transferred onto the recording material P all at once by the secondary transfer roller 24 to which a secondary transfer bias (opposite polarity (positive polarity) with respect to toner) is applied. The recording material P on which the full-color toner image is formed is conveyed to the fixing device 12, and the full-color toner image is heated and pressed at the fixing nip portion between the fixing roller 12a and the pressure roller 12b to form the surface of the recording material P. It is fixed by heat and discharged to the outside. Thus, a series of image forming operations is completed.

  At the time of the primary transfer, the primary transfer residual toner remaining on the photosensitive drum 2 is removed and collected by the drum cleaning device 6. The secondary transfer residual toner remaining on the intermediate transfer belt 20 after the secondary transfer is collected by the ICL roller 30 as follows.

  The secondary transfer residual toner is simultaneously charged by bringing the ICL roller 30 into contact with the intermediate transfer belt 20 and applying a bias from a cleaning power source (not shown). The secondary transfer residual toner after the secondary transfer is forcibly charged to a polarity opposite to the toner (positive polarity) by the discharge at the ICL roller 30 and collected.

(2) Primary transfer mechanism The primary transfer mechanism will be described.

  FIG. 2 is a perspective view showing a primary transfer mechanism in the image forming unit 1Y. As shown in FIG. 2, the elastic member 15a is made of PET resin and has a sheet shape of 8.5 mm in length and 225 mm in width (longitudinal width direction).

  The transfer sheet 5a is made of a conductive nylon resin and has a substantially rectangular shape with a length of 9.5 mm and a width of 225 mm.

As a resistance value, a ground electrode corresponding to the contact surface is attached to the contact surface side of the transfer sheet 5 a with the intermediate transfer belt 20. The one having a resistance value of 1 × 10 ⁶ Ω when 25 V is applied between both electrodes of the transfer voltage electrode to which the transfer voltage is applied is used.

  The thickness of the transfer sheet 5a was 150 μm. The thickness of the transfer sheet 5a is preferably 40 μm or more and 400 μm or less. The thinner the transfer sheet 5a is, the easier it is to follow the shape of the elastic member 15a and the nip shape is more stable. The thicker the transfer sheet 5a, the harder it is to stretch and the occurrence of waves. However, it is difficult to follow the shape of the elastic member 15a, the nip shape tends to become unstable, and transfer defects (corresponding to contact unevenness) Uneven transfer) is likely to occur.

  FIG. 3 is a perspective view of the transfer unit holding member 16a in the image forming unit 1Y.

  The transfer portion holding member 16 a has a flat holding surface in a shape inclined by 45 ° from the tangential direction of the photosensitive drum 2 a and the intermediate transfer belt 20. The material of the transfer holding member 16a is made of a conductive resin, and also serves as a power supply member for a primary transfer bias applied from the primary transfer power supply 40a in the present embodiment.

  FIG. 4 shows a schematic diagram of a primary transfer mechanism in the image forming unit 1Y.

  As shown in FIG. 4, the transfer sheet 5a has a 9.5 mm vertical transfer sheet 5a attached to the upstream side surface of the elastic member 15a with a double-sided tape (attached at a position from the ridgeline B to 3 mm). By bending the elastic member 15a and the transfer sheet 5a using elasticity, the belt-side contact surface portion of the elastic member 15a can be contacted to the intermediate transfer belt 20 with the transfer sheet 5a covering it.

  At the time of application to the double-sided tape, one end portion side of the transfer sheet 5a (the end portion side not in contact with the intermediate transfer belt 20) is arranged on the substantially ridge line B. The central portion in the width direction (belt width direction central portion) of the transfer sheet 5a is warped toward the photosensitive drum by h (h = 0.2 mm) with respect to the straight ridge line B as a reference.

  Here, when the length of the transfer sheet 5a in the sheet width direction is L and the amount of warpage of the transfer sheet 5a (the amount of dent in the center with respect to the end in the sheet width direction) is h, h / L is 0.0002 or more and 0 .004 or less.

  As a result, the transfer sheet 5a is warped in the direction away from the photoconductor drum 2 from the center to the both ends in the width direction of the transfer sheet 5a on the photosensitive drum side (the end side in contact with the intermediate transfer belt 20). It becomes a shape. That is, the upstream side of the transfer sheet 5a in the rotational direction of the intermediate transfer belt (the upstream side of the endless belt member in the rotational direction) warps in a concave shape.

  As a result, at the contact surface side of the intermediate transfer belt 20 and the transfer sheet 5a, both end portions are warped so as to be pulled toward the upstream upstream side of the intermediate transfer belt relative to the central portion in the width direction of the transfer sheet 5a. As a result, it is possible to exert a force to shrink the belt in the longitudinal direction of the transfer sheet 5a in the rotation direction of the intermediate transfer belt 20 (direction perpendicular to the belt width direction).

  The warp amount h of the central portion of the transfer sheet 5a is preferably 45 μm or more and 900 μm or less. As the amount of warpage of the transfer sheet 5a is increased, the waviness can be suppressed, but the bent portion of the transfer sheet 5a tends to become unstable. For this reason, the nip shape is likely to be unstable, and transfer defects (transfer unevenness corresponding to contact unevenness) are likely to occur. The smaller the amount of warping of the transfer sheet 5a, the more stable the nip shape is, and it becomes easier to suppress transfer defects, but waves are more likely to occur.

  The other image forming units 1M, 1C, and 1Bk have the same configuration.

(3) Image Output Experiment Result of Image Forming Apparatus of Present Embodiment Next, the result of the image output experiment of the image forming apparatus of the present embodiment will be described.

  As an image formation endurance test, CLC color laser copier paper (Canon sales, product name) was used as a recording material, and 100,000 sheets were printed using an image with a CMYK color printing rate of 4%. Image sampling was performed at the start of durability and every 10,000 sheets thereafter. The atmosphere environment in which the experiment was performed is a temperature of 23 ° C. and a humidity of 50%.

  A plain paper mode is used as the print mode. In the image forming apparatus used in the experiment, the process speed is 100 mm / sec and the throughput is 18 sheets per minute.

  As the sampling images, solid images, halftone images, and character thin line images were output in CMYKRBG colors.

  Image evaluation was performed from the sampled images, and ranking evaluation was performed from the viewpoint of the following four image defects ((1) scattering, (2) peeling discharge, and (3) transfer uniformity).

  As a rank, ranking was performed with ◯ when no image defect occurred, △ when slightly confirmed, △ when confirmed, △ × when slightly bad, and × when bad.

  FIG. 5 shows the evaluation results. As shown in FIG. 5, in the image forming apparatus of this embodiment, no image defect occurred through the endurance of 100,000 sheets.

(4) Results of Image Output Experiments of Image Forming Apparatuses of Comparative Examples 1 to 3 Next, results of image output experiments of image forming apparatuses of Comparative Examples 1 to 3 such as a conventional example will be described. As the image formation durability test method and evaluation method, the same method as described above was used.

  As Comparative Example 1, an image forming apparatus using a primary transfer mechanism attached without warping the transfer sheet was used.

  As Comparative Example 2, an image forming apparatus using a primary transfer mechanism in which a transfer brush is brought into contact with the intermediate transfer belt 20 (the contact area is the same as that of a transfer sheet) was used.

  As Comparative Example 3, an image forming apparatus using a primary transfer mechanism in which a transfer roller is in contact with an intermediate transfer belt was used.

  FIG. 6 shows the evaluation results. As shown in FIG. 6, in Comparative Example 1, transfer failure was confirmed from the point where the durable number exceeded 80,000.

  In Comparative Example 2, peeling discharge was confirmed when the durable number exceeded 50,000, and scattering and transfer failure were confirmed when the number exceeded 70,000.

  In Comparative Example 3, the level of splattering through durability was slightly worse. Further, peeling discharge was confirmed from a place exceeding 70,000 sheets, and a transfer defect was confirmed from a place exceeding 90,000 sheets.

(effect)
As described above, on the downstream side of the transfer sheet 5a in the rotational direction of the intermediate transfer belt, by applying the force for contracting in the longitudinal direction to both ends in the width direction of the transfer sheet 5a, transfer is performed not only in the initial stage of image formation but also in the later stage. Generation of the wave of the sheet 5a can be suppressed.

  Thereby, the pre-transfer can be suppressed from the initial use to the later stage without increasing the size and cost of the apparatus with a simple configuration, and the deterioration of the image quality can be suppressed. Even if there is no neutralizing member on the back surface of the intermediate transfer belt or the transfer belt, the peeling discharge can be suppressed and a high quality image can be obtained.

[Second Embodiment]
Next, a second embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. About the part which overlaps with said 1st embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  FIG. 7 is a perspective view showing a primary transfer mechanism according to the present embodiment. FIG. 8 is a schematic view showing a state in which the transfer portion holding member 16a is viewed from the contact surface side with the intermediate transfer belt 20.

  As shown in FIGS. 7 and 8, the image forming apparatus of the present embodiment is provided with a transfer unit holding member 26 (26a, 26b, 26c, 26d) instead of the transfer unit holding member 16 of the first embodiment. Is.

  The transfer portion holding member 26a is upstream in the rotation direction of the intermediate transfer belt 20 by h (h = 0.2 mm) at both ends in the sheet width direction with respect to the central portion in the sheet width direction on the upstream side in the rotation direction of the intermediate transfer belt. It has a reverse crown shape.

  The elastic member 15a and the transfer sheet 5a are attached to the transfer portion holding member 26a in accordance with the shape of the transfer portion holding member 26a. As a result, on the contact surface side of the intermediate transfer belt 20 and the transfer sheet 5a, the end side warps so as to be pulled upstream in the intermediate transfer belt rotation direction, compared to the sheet width direction center of the transfer sheet 5a. . Thereby, a force for contracting in the longitudinal direction can be exerted on the downstream side of the transfer sheet 5a in the rotation direction of the intermediate transfer belt.

  With this configuration, as in the first embodiment, an image is applied by applying a force to shrink in the longitudinal direction at both ends in the width direction of the transfer sheet 5a on the downstream side in the rotational direction of the intermediate transfer belt of the transfer sheet 5a. It is possible to suppress the occurrence of waves in the transfer sheet 5a not only in the initial stage of formation but also in the later stage.

  Thereby, the pre-transfer can be suppressed from the initial use to the later stage without increasing the size and cost of the apparatus with a simple configuration, and the deterioration of the image quality can be suppressed. Even if there is no neutralizing member on the back surface of the intermediate transfer belt or the transfer belt, the peeling discharge can be suppressed and a high quality image can be obtained.

[Third embodiment]
Next, a third embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. About the part which overlaps with said 1st embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  FIG. 9 is a perspective view showing the primary transfer mechanism according to the present embodiment. As shown in FIG. 9, the image forming apparatus of this embodiment is provided with an elastic member (holding member) 35 instead of the elastic member 15 and the transfer unit holding member 16 of the first embodiment.

  The elastic member 35a is a foamed sponge-like elastic body made of urethane foam sponge layer, 5 mm in length (intermediate transfer belt rotational movement direction), 225 mm in width (longitudinal width direction), and 5 mm in height (relative to the contact surface of the intermediate transfer belt). (Vertical direction).

As a resistance value, a resistance when a ground electrode corresponding to the contact surface is attached to the contact surface side of the elastic member 35a with the intermediate transfer belt 20 and 100 V is applied between both electrodes of the transfer voltage electrode to which the transfer voltage is applied. A value of 4 × 10 ⁶ Ω is used.

  The hardness is 30 ° as measured by Asker C (500 gf) on the contact surface side of the elastic member 35 a with the intermediate transfer belt 20.

  The transfer sheet 5a is formed of PE having conductivity, and has a substantially rectangular shape with a length of 9.5 mm and a width of 225 mm. The thickness of the transfer sheet 5a was 350 μm.

The resistance value is a resistance when a ground electrode corresponding to the contact surface is attached to the contact surface side of the transfer sheet 5a with the intermediate transfer belt 20, and 25V is applied between both electrodes of the transfer voltage electrode to which the transfer voltage is applied. A value of 1 × 10 ⁶ Ω is used.

  FIG. 10 is a schematic diagram of a primary transfer mechanism in the image forming unit 1Y. As shown in FIG. 10, the transfer sheet 5a is attached to the side surface of the elastic member 35a on the upstream side in the intermediate transfer belt rotation direction with a double-sided tape (attached at a position from the ridgeline B to 3 mm). The transfer sheet 5a is folded at a ridge line A portion (the height of the elastic member 35a) of approximately 5 mm. By folding back at the ridge line A, the belt-side contact surface portion of the elastic member 35a can be brought into contact with the intermediate transfer belt 20 in a state where the entire surface is covered with the transfer sheet 5a.

  At the time of application to the double-sided tape, one end portion side of the transfer sheet 5a (the end portion side not in contact with the intermediate transfer belt 20) is arranged on the substantially ridge line B.

  The central portion in the width direction (belt width direction central portion) of the transfer sheet 5a is warped toward the photosensitive drum by h (h = 0.2 mm) with respect to the straight ridge line B as a reference.

  As a result, the transfer sheet 5a is warped in the direction away from the photoconductor drum 2 from the center to the both ends in the width direction of the transfer sheet 5a on the photosensitive drum side (the end side in contact with the intermediate transfer belt 20). It becomes a shape.

  As a result, at the contact surface side of the intermediate transfer belt 20 and the transfer sheet 5a, both end portions are warped so as to be pulled toward the upstream upstream side of the intermediate transfer belt relative to the central portion in the width direction of the transfer sheet 5a. As a result, it is possible to exert a force to shrink the belt in the longitudinal direction of the transfer sheet 5a in the rotation direction of the intermediate transfer belt 20 (direction perpendicular to the belt width direction).

  The warp amount h of the central portion of the transfer sheet 5a is preferably 45 μm or more and 900 μm or less. As the amount of warpage of the transfer sheet 5a is increased, the waviness can be suppressed, but the bent portion of the transfer sheet 5a tends to become unstable. For this reason, the nip shape is likely to be unstable, and transfer defects (transfer unevenness corresponding to contact unevenness) are likely to occur. The smaller the amount of warping of the transfer sheet 5a, the more stable the nip shape is, and it becomes easier to suppress transfer defects, but waves are more likely to occur.

  The other image forming units 1M, 1C, and 1Bk have the same configuration.

  With this configuration, as in the first embodiment, an image is applied by applying a force to shrink in the longitudinal direction at both ends in the width direction of the transfer sheet 5a on the downstream side in the rotational direction of the intermediate transfer belt of the transfer sheet 5a. It is possible to suppress the occurrence of the wave of the transfer sheet 5a not only in the initial stage of formation but also in the later stage.

  Thereby, the pre-transfer can be suppressed from the initial use to the later stage without increasing the size and cost of the apparatus with a simple configuration, and the deterioration of the image quality can be suppressed. Even if there is no neutralizing member on the back surface of the intermediate transfer belt or the transfer belt, the peeling discharge can be suppressed and a high quality image can be obtained.

[Fourth embodiment]
Next, a fourth embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. Portions that are the same as those described in the first and third embodiments will be given the same reference numerals and description thereof will be omitted.

  FIG. 11 is a perspective view showing a primary transfer mechanism according to the present embodiment. As shown in FIG. 11, the image forming apparatus of the present embodiment is provided with an elastic member (holding member) 45a instead of the elastic member 35a of the third embodiment.

  Similar to the elastic member 35a, the elastic member 45a is a foamed sponge-like elastic body of urethane 5 mm in length (intermediate transfer belt rotational movement direction), 225 mm in width (longitudinal width direction), and 5 mm in height (on the intermediate transfer belt contact surface). It is a substantially rectangular parallelepiped shape.

The elastic member 45a has a crown shape that protrudes downstream in the intermediate transfer belt rotation direction by h (h = 0.2 mm) with respect to the rotation direction of the intermediate transfer belt 20 with the center portion in the sheet width direction as a reference from both ends in the sheet width direction. It is a thing.

  By attaching the transfer sheet 5a to the elastic member 45a, as in the first embodiment, on the downstream side of the transfer sheet 5a in the rotational direction of the intermediate transfer belt, the transfer sheet 5a is contracted in the longitudinal direction at both ends in the width direction. By using this force, it is possible to suppress the occurrence of the wave of the transfer sheet 5a not only in the initial stage of image formation but also in the later stage.

  Thereby, the pre-transfer can be suppressed from the initial use to the later stage without increasing the size and cost of the apparatus with a simple configuration, and the deterioration of the image quality can be suppressed. Even if there is no neutralizing member on the back surface of the intermediate transfer belt or the transfer belt, the peeling discharge can be suppressed and a high quality image can be obtained.

[Fifth embodiment]
Next, a fifth embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. Portions that are the same as those described in the first and third embodiments will be given the same reference numerals and description thereof will be omitted.

  FIG. 12 is a perspective view showing a primary transfer mechanism according to the present embodiment. As shown in FIG. 12, the image forming apparatus according to this embodiment has a transfer portion holding member 56a attached to the side surface on the upstream side in the intermediate transfer belt rotation direction of the elastic member 35a according to the third embodiment. The transfer portion holding member 56a is made of metal and also serves as a power supply member for a primary transfer bias applied from the primary transfer power supply 40a.

  FIG. 13 is a schematic view showing a state in which the transfer portion holding member 56a is viewed from the contact surface side with the intermediate transfer belt 20. As shown in FIG. 13, the transfer portion holding member 56a has an inverted crown shape (end) so that the end thereof is h (h = 0.2 mm) upstream in the intermediate transfer belt rotation direction with respect to the central portion in the sheet width direction. 1.0 mm at the center and 0.8 mm at the center).

  The height of the transfer portion holding member 56a (the length in the direction perpendicular to the contact surface of the intermediate transfer belt) is 4 mm, and the transfer portion holding member 56a does not push the intermediate transfer belt 20 via the transfer sheet 5a. .

  By attaching the transfer sheet 5a to the transfer portion holding member 56a, the end portion of the transfer sheet 5a rotates on the contact surface side of the intermediate transfer belt 20 and the transfer sheet 5a as compared with the central portion in the sheet width direction. Warps to be pulled upstream in the direction.

  With this configuration, as in the first embodiment, an image is applied by applying a force to shrink in the longitudinal direction at both ends in the width direction of the transfer sheet 5a on the downstream side in the rotational direction of the intermediate transfer belt of the transfer sheet 5a. It is possible to suppress the occurrence of the wave of the transfer sheet 5a not only in the initial stage of formation but also in the later stage.

  Thereby, the pre-transfer can be suppressed from the initial use to the later stage without increasing the size and cost of the apparatus with a simple configuration, and the deterioration of the image quality can be suppressed. Even if there is no neutralizing member on the back surface of the intermediate transfer belt or the transfer belt, the peeling discharge can be suppressed and a high quality image can be obtained.

[Sixth embodiment]
Next, a sixth embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. Portions that are the same as those described in the first and third embodiments will be given the same reference numerals and description thereof will be omitted.

  FIG. 14 is a perspective view showing a primary transfer mechanism according to the present embodiment. As shown in FIG. 14, the image forming apparatus according to the present embodiment has a transfer portion holding member 66a attached to the side surface of the elastic member 35a of the third embodiment on the upstream side in the rotational direction of the intermediate transfer belt.

  The transfer portion holding member 66a has a substantially trapezoidal columnar shape with an upper base of 1 mm, a lower base of 5 mm, a lateral width of 225 mm (length in the sheet width direction), and a height of 4 mm (length in the direction perpendicular to the contact surface of the intermediate transfer belt). The upper base is the length of the intermediate transfer belt in the rotational direction on the intermediate transfer belt side. The lower base is the length of the surface facing the upper base in the rotation direction of the intermediate transfer belt.

  The transfer portion holding member 66a is made of metal and also serves as a power supply member for a primary transfer bias applied from the primary transfer power supply 40a. The height of the transfer portion holding member 66a is such that the transfer portion holding member 66a does not push the intermediate transfer belt 20 via the transfer sheet 5a.

  The transfer sheet 5a has a substantially rectangular shape with a length of 11.5 mm and a width of 225 mm. The transfer sheet 5a is attached to the transfer unit holding member 66a. At this time, on the inclined surface side of the transfer portion holding member 66a, the central portion is h (h = 0.2 mm) from the end portion on the inclined surface of the transfer portion holding member 66a with respect to the end portion in the sheet width direction of the transfer sheet 5a. It is warped so as to be in the direction of the photosensitive drum, and is formed into an inverted crown shape.

  As a result, the transfer sheet 5a is warped in the direction away from the photoconductor drum 2 from the center to the both ends in the width direction of the transfer sheet 5a on the photosensitive drum side (the end side in contact with the intermediate transfer belt 20). It becomes a shape.

  With this configuration, as in the first embodiment, an image is applied by applying a force to shrink in the longitudinal direction at both ends in the width direction of the transfer sheet 5a on the downstream side in the rotational direction of the intermediate transfer belt of the transfer sheet 5a. It is possible to suppress the occurrence of the wave of the transfer sheet 5a not only in the initial stage of formation but also in the later stage.

  Thereby, the pre-transfer can be suppressed from the initial use to the later stage without increasing the size and cost of the apparatus with a simple configuration, and the deterioration of the image quality can be suppressed. Even if there is no neutralizing member on the back surface of the intermediate transfer belt or the transfer belt, the peeling discharge can be suppressed and a high quality image can be obtained.

[Seventh embodiment]
Next, a seventh embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. Parts that are the same as those described in the first and sixth embodiments are denoted by the same reference numerals and description thereof is omitted.

  FIG. 15 is a perspective view showing a primary transfer mechanism according to the present embodiment. As shown in FIG. 15, the image forming apparatus of the present embodiment is provided with a transfer unit holding member 76a instead of the transfer unit holding member 66a of the sixth embodiment.

  The transfer portion holding member 76a has a substantially trapezoidal columnar shape with an upper base of 1 mm, a lower base of 5 mm, a lateral width of 225 mm (length in the sheet width direction), and a height of 4 mm (length in the direction perpendicular to the contact surface of the intermediate transfer belt). . The upper base is the length of the intermediate transfer belt in the rotational direction on the intermediate transfer belt side. The lower base is the length of the surface facing the upper base in the rotation direction of the intermediate transfer belt. The height of the transfer portion holding member 76a (distance perpendicular to the contact surface of the intermediate transfer belt) is such that the transfer portion holding member 76a does not push the intermediate transfer belt 20 via the transfer sheet 5a. .

  FIG. 16 is a schematic view showing the transfer portion holding member 76a. FIG. 16B is a cross-sectional view of the transfer unit holding member 76a taken along an arbitrary plane parallel to the contact surface between the intermediate transfer belt 20 and the transfer sheet 5a. As shown in FIG. 16, the inclined surface of the substantially trapezoidal columnar shape has an inverted crown shape. The transfer portion holding member 76a has an inverse crown shape such that the end thereof is h (h = 0.2 mm) upstream in the intermediate transfer belt rotation direction with respect to the central portion in the sheet width direction.

  The transfer sheet 5a has a substantially rectangular shape with a length of 11.5 mm and a width of 225 mm. By attaching the transfer sheet 5a to the transfer part holding member 76a, both ends of the contact surface side between the intermediate transfer belt 20 and the transfer sheet 5a are upstream of the intermediate transfer belt in the rotation direction compared to the central part of the transfer sheet 5a. Warp to be pulled by.

  With this configuration, as in the first embodiment, an image is applied by applying a force to shrink in the longitudinal direction at both ends in the width direction of the transfer sheet 5a on the downstream side in the rotational direction of the intermediate transfer belt of the transfer sheet 5a. It is possible to suppress the occurrence of the wave of the transfer sheet 5a not only in the initial stage of formation but also in the later stage.

  Thereby, the pre-transfer can be suppressed from the initial use to the later stage without increasing the size and cost of the apparatus with a simple configuration, and the deterioration of the image quality can be suppressed. Even if there is no neutralizing member on the back surface of the intermediate transfer belt or the transfer belt, the peeling discharge can be suppressed and a high quality image can be obtained.

[Eighth embodiment]
Next, an image forming apparatus according to an eighth embodiment of the invention will be described with reference to the drawings. Portions that are the same as those described in the first and third embodiments will be given the same reference numerals and description thereof will be omitted.

  FIG. 17 is a schematic configuration diagram of an image forming apparatus (electrophotographic tandem type full color printer) according to the present embodiment. As shown in FIG. 17, the image forming apparatus of this embodiment is a tandem type color image forming apparatus that sequentially superimposes and transfers toner images of each color formed on each of the four photosensitive drums onto a recording material. The primary transfer mechanism of the third embodiment is applied.

  The color image forming apparatus includes four image forming units (image forming units) 1Y, 1M, 1C, and 1Bk that form yellow, magenta, cyan, and black images. The four image forming units are arranged in a row at a constant interval.

  The primary transfer mechanism in the image forming unit 1 has the same configuration as that of the third embodiment, but instead of the intermediate transfer belt 20, a recording material conveyance belt (endless belt member) 80 as a recording material carrier is provided. It is used.

  The elastic member 35 a is in contact with the transfer sheet 5 a and urges each photosensitive drum 2 a via the recording material conveyance belt 80. The other image forming units 1M, 1C, and 1Bk have the same configuration.

  The recording material conveyance belt 80 is stretched between the driving roller 21 and the support roller 37, and is rotated (moved) in the arrow direction (clockwise) by the driving of the driving roller 21. On the upstream side of the image forming unit 1Y on the recording material conveyance belt 80, an adsorption roller 36 for electrostatically adsorbing the recording material P as a transfer medium on the recording material conveyance belt 80 is installed.

  A fixing device 12 having a fixing roller 12a and a pressure roller 12b is installed on the downstream side of the image forming unit 1Bk in the recording material conveyance direction of the recording material conveyance belt 80.

  Next, an image forming operation by the color image forming apparatus of the present embodiment will be described.

  The formation of the developed image on each of the image forming units 1Y, 1M, 1C, and 1Bk is the same as that in the first embodiment, and a description thereof will be omitted.

  The recording material P is conveyed by a feeding roller (registration roller) 13 in accordance with the development image formation timing. The transported recording material P is electrostatically attracted to the surface of the recording material transport belt 80 moved by driving of the driving roller 21 by the suction roller 36 to which an suction bias (opposite polarity (positive polarity) to toner) is applied. . The adsorbed recording material P is conveyed to the transfer nip portion N of the image forming unit 1Y, and the yellow toner image is transferred by the transfer sheet 5a to which the transfer bias (opposite polarity (positive polarity) from the toner) is applied. .

  The recording material P to which the yellow toner image has been transferred is moved to the image forming unit 1M side while being adsorbed on the surface of the recording material conveyance belt 80. Similarly, in the transfer portion nip N of the image forming portion 1M, a magenta toner image similarly formed on the photosensitive drum 2b is overlaid on the yellow toner image, and a transfer bias (a polarity opposite to the toner (positive polarity) is obtained. )) Is applied to the transfer sheet 5b.

  In the same manner, the yellow and magenta toner images superimposed and transferred onto the recording material P are sequentially overlapped to form a full-color toner image on the recording material P.

  The recording material P on which the full-color toner image is formed is separated from the surface of the recording material conveyance belt 80 and conveyed to the fixing device 12. After the toner image is fixed, the recording material P is discharged to the outside and a series of image forming operations is completed. To do.

  The recording material conveyance belt 80 does not normally carry a toner image directly on the surface. However, it is detected directly on the recording material conveyance belt 80 during operation such as density detection or color registration correction due to the contamination toner adhering to the recording material conveyance belt 80 due to a jam or fog on the non-image area. May carry a patch. In order to clean the toner on the recording material conveyance belt 80, a cleaning process is performed at a predetermined timing. In the cleaning step, each image forming unit 1 applies a cleaning bias having a polarity opposite to that at the time of transfer to the transfer sheet 5 to transfer the contaminated toner on the recording material conveyance belt 80 to the photosensitive drum 2, and the drum cleaning device. 6 is performed by collecting.

  Also in this embodiment, the same effect as the above embodiment can be obtained. That is, with a simple configuration, pre-transfer can be suppressed from the initial use to the later stage without causing an increase in size and cost of the apparatus, and deterioration in image quality can be suppressed. Even if there is no neutralizing member on the back surface of the intermediate transfer belt or the transfer belt, the peeling discharge can be suppressed and a high quality image can be obtained.

  In each of the above-described embodiments, the description has been made using the intermediate transfer type and tandem transfer type color image forming apparatuses. However, the present invention is not limited to such a configuration. For example, the present invention can be applied to a configuration using a transfer sheet in a similar configuration, such as a monochrome image forming device using a recording material conveyance belt or a color image forming device using a recording material conveyance belt in an intermediate transfer system.

  In each of the above-described embodiments, the shape of the transfer sheet is described as a rectangle (that is, the end is a straight line), and the method for curving the end of the transfer sheet is described. However, the transfer sheet may not be a rectangle. For example, the structure which an edge part becomes a curve may be sufficient.

  Further, in each of the above-described embodiments, as a method of warping the transfer sheet, the transfer sheet is placed against a substantially planar arrangement target while being warped in an inverted crown shape, or attached to an inverted crown-shaped curved object. The method of attaching and warping was explained. The present invention may have a combination of both.

  Further, in each of the above-described embodiments, the reverse crown shape has been described as the method of warping the transfer sheet. However, the transfer sheet may be warped in a concave shape by other methods such as a taper shape.

1 is a schematic configuration diagram illustrating a color image forming apparatus according to a first embodiment. It is a perspective view which shows a primary transfer mechanism. It is a perspective view of a transfer part holding member. It is the schematic of a primary transfer mechanism. It is a figure which shows an evaluation result. It is a figure which shows an evaluation result. It is a perspective view which shows the primary transfer mechanism which concerns on 2nd embodiment. FIG. 6 is a schematic diagram illustrating a state in which a transfer unit holding member is viewed from a contact surface side with an intermediate transfer belt. It is a perspective view which shows the primary transfer mechanism which concerns on 3rd embodiment. It is the schematic of a primary transfer mechanism. It is a perspective view which shows the primary transfer mechanism which concerns on 4th embodiment. It is a perspective view which shows the primary transfer mechanism which concerns on 5th embodiment. FIG. 6 is a schematic diagram illustrating a state in which a transfer unit holding member is viewed from a contact surface side with an intermediate transfer belt. It is a perspective view which shows the primary transfer mechanism which concerns on 6th embodiment. It is a perspective view which shows the primary transfer mechanism which concerns on 7th embodiment. It is the schematic which shows a transfer part holding member. It is a schematic block diagram of the image forming apparatus which concerns on 8th embodiment. FIG. 6 is a cross-sectional configuration diagram using a transfer roller as a transfer member. FIG. 6 is a cross-sectional configuration diagram using a transfer brush as a transfer member. FIG. 6 is a cross-sectional configuration diagram using a transfer sheet as a transfer member.

Explanation of symbols

B ... Ridge line M ... Secondary transfer part N ... Primary transfer part N1, N2 ... Contact area P ... Recording material 1 ... Image forming part 2 ... Photosensitive drum (image carrier)
3 ... charging roller 4 ... developing device 5 ... transfer sheet (sheet-like transfer member)
6 ... Drum cleaning device 7 ... Exposure device 12 ... Fixing device 12a ... Fixing roller 12b ... Pressure roller 13 ... Feeding roller 15 ... Elastic member (pressing member)
16, 26, 56, 66, 76 ... transfer portion holding member 20 ... intermediate transfer belt (endless belt member)
DESCRIPTION OF SYMBOLS 21 ... Drive roller 23 ... Secondary transfer counter roller 24 ... Secondary transfer roller 30 ... Charging roller 35 ... Elastic member 36 ... Adsorption roller 37 ... Support roller 40a ... Primary transfer power supply 80 ... Recording material conveyance belt (endless belt) Element)

Claims (7)

An image carrier that carries a toner image, a rotatable endless belt member that conveys a toner image transferred from the image carrier, and the contact surface of the endless belt member that corresponds to the contact surface of the image carrier. a transfer means for contacting to the back surface of the endless belt member, the image forming apparatus to which the toner image is transferred from said image bearing member by said transfer means to which a voltage is applied to the endless belt side,
It said transfer means is in contact with the back surface of the endless belt member, wherein the transfer sheet is pressed in the direction of the endless belt member, wherein the transfer sheet at the free end the other end one end fixed, and The free end is disposed downstream of the endless belt member in the rotational direction;
The holding member holds one end side of the transfer sheet, and the holding member has the endless belt member in a central direction of the holding member rather than both end sides with respect to a longitudinal direction perpendicular to the moving direction of the endless belt member. The one end side of the transfer sheet is supported by one end side of the transfer sheet by the holding member, and the end side of the transfer sheet is downstream in the rotation direction of the endless belt member than the both end sides. An image forming apparatus, wherein the shape is changed to a shape protruding to the side . The image forming apparatus according to claim 1, wherein the transfer unit includes an elastic member that presses the transfer sheet toward the endless belt member. The image forming apparatus according to claim 1, wherein the transfer sheet has a thickness of 40 μm or more and 400 μm or less. The image forming apparatus according to claim 1, wherein the transfer sheet and the holding member are bonded by a double-sided tape . The image forming apparatus according to claim 1 , wherein a voltage is applied to the transfer sheet through the holding member . The image forming apparatus according to claim 1, wherein the endless belt member is an intermediate transfer belt to which a toner image is transferred from the image carrier. The image forming apparatus according to claim 1, wherein the endless belt member is a conveyance belt that conveys a recording material onto which a toner image is transferred from the image carrier.

Images