JP4465178B2 - Image forming apparatus - Google Patents

Description

  The present invention provides a transfer material transport member that transports a transfer material so as to pass a transfer position to which a toner image on an image carrier is transferred, and a transfer bias is applied from the back surface of the transfer material transport member at the transfer position. The present invention relates to an image forming apparatus including a transfer bias applying member.

  Conventionally, a plurality of toner image forming portions each having a photosensitive drum or the like as an image carrier are arranged in parallel along a transfer conveyance belt as a transfer material conveyance member that conveys and conveys transfer paper as a transfer material. There is a tandem image forming apparatus. A transfer bias applying member is provided at a position facing each photoconductor drum across the transfer conveyance belt so as to contact the back surface of the transfer conveyance belt. A transfer bias is applied from the transfer bias applying member, and the toner images on the respective photoconductive drums are sequentially electrostatically transferred onto a transfer sheet to form a color image.

When the transfer paper is separated from the transfer / conveying belt, the toner may scatter and cause image deterioration. Therefore, as shown in FIG. 6, among the support rollers around which the transfer conveyance belt is wound, a support roller (hereinafter referred to as a separation roller) located at a position where the transfer paper 100 is separated from the transfer conveyance belt 160 is opposite to the toner. A device that applies a polar bias is known (for example, Patent Document 1). Thus, the toner is electrostatically adsorbed to the transfer paper 100, so that the toner can be prevented from scattering when the transfer paper is separated from the transfer conveyance belt.
In the case of the tandem type image forming apparatus described above, when the leading edge of the transfer paper reaches the separation roller 162, a part of the transfer paper 100 exists at the position of the photosensitive drum 111K adjacent to the separation roller 162, and the toner image is electrostatically charged. It has been transcribed. Under normal circumstances, the transfer paper 100 and the transfer conveyance belt 160 have high resistance, and the distance between the separation roller 162 and the photosensitive drum 111K is sufficiently large, as shown in FIG. No current flows from the separation roller 162 through the transfer paper 100 or the transfer conveyance belt 160 to the photosensitive drum 111K adjacent to the separation roller 162. On the other hand, since the distance between the transfer bias applying member 167K and the photosensitive drum 111K is short, a current flows only between the transfer bias and the photosensitive drum.

JP 2001-356611 A

  However, if the transfer paper becomes damp and the resistance becomes low in a high humidity environment or the like, the insulation state between the transfer paper 100 and the photosensitive drum 111K cannot be maintained, as shown by the arrow in FIG. In addition, a current flows from the separation roller 162 through the transfer paper 100 to the transfer position. As a result, the transfer current that flows to the transfer position becomes an overcurrent, and the polarity of some of the toner is reversed, and an abnormal image such as density unevenness may occur without being electrostatically attracted to the transfer paper.

  The present invention has been made in view of the above problems, and an object of the present invention is to form an image capable of obtaining a good image even when the transfer paper is damp and has low resistance in a high humidity environment or the like. Is to provide a device.

In order to achieve the above object, the invention of claim 1 includes a plurality of image carriers that carry toner images charged to a predetermined polarity, and a plurality of transfer positions to which the toner images on these image carriers are transferred. An endless transfer material conveyance belt that conveys the transfer material so as to pass sequentially, and a plurality of abutting on the back surface of the transfer material conveyance belt, and rotatably driving the transfer material conveyance belt while stretching the transfer material In the image forming apparatus comprising a tension roller and a plurality of transfer bias applying members that are arranged at each transfer position and apply a transfer bias from the back surface of the transfer material transport member at the transfer position, the transfer material transport The surface resistivity of the belt is 1E + 12 [Ω / □] or more, and the transfer material transports the transfer material among the plurality of stretching rollers in order to suppress toner scattering when the transfer material is separated from the transfer transport belt. Belt The separation roller is a tension roller which is located spaced apart position comprises a separation bias power source for applying a charging polarity opposite the separation bias of the toner image, the current value is the transfer bias applying member flowing through the separation roller A current limiter for limiting the current flowing through the separation roller is provided so as to be smaller than a current value flowing through the separation roller.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the transfer rate at which the toner image on the image carrier is transferred to the transfer material is 90% or more.
According to a third aspect of the present invention, in the image forming apparatus of the second aspect, the current value flowing through the separation roller is set to a transfer rate at which the toner image on the image carrier is transferred to a transfer material is 90% or more. The current limiter is set so as to limit it to ½ or less of a difference value between an upper limit value and a lower limit value of a range of transfer current flowing to the transfer position.
According to a fourth aspect of the present invention, in the image forming apparatus of the second aspect, the current limiter is configured such that a sum of a current value flowing through the separation roller and a current value flowing through the transfer bias applying member is on the image carrier. The current flowing through the separation roller is limited so that the transfer rate at which the toner image is transferred to the transfer material is 90% or more and is not more than the upper limit of the range of the transfer current value flowing at the transfer position. Is.
According to a fifth aspect of the present invention, in the image forming apparatus of the first, second, third, or fourth aspect, the current limiter is set so that a current value flowing through the separation roller is 1 μA or less. It is.
The invention of claim 6 is the image forming apparatus 請 Motomeko 1, 2, 3, 4 or 5, to the transfer material conveyance belt, is formed with a detected portion, detects該被detection unit It is characterized by having a detecting means for performing.
The invention of claim 7 is the image forming apparatus according to claim 2, 3, 4, 5 or 6, the divided release roller, together with a metal roller, is driven to rotate the transfer material conveyance belt drive The roller is other than the separation roller.

According to the first to seventh aspects of the invention, the current value flowing through the separation roller is controlled by the current limiter so as to be smaller than the current value flowing through the transfer bias applying member. As a result, even if the transfer material is damp and the resistance is low, and the current flows from the separation roller through the transfer material to the transfer position, the transfer current is suppressed from being overcurrent. Therefore, it is possible to suppress the polarity of some of the toner from being reversed and not being electrostatically attracted to the transfer paper. As a result, there is an effect that abnormal images such as density unevenness do not occur.

Hereinafter, an embodiment in which the present invention is applied to a direct transfer tandem type laser printer (hereinafter referred to as “laser printer”) as an electrophotographic image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram of a schematic configuration of a laser printer according to the present embodiment. This laser printer includes toner image forming units 1Y, 1M, and 1C as four sets of image forming units for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). 1K. Hereinafter, the subscripts Y, M, C, and K of the respective symbols indicate members for yellow, magenta, cyan, and black, respectively. The four sets of toner image forming portions 1Y, 1M, 1C, and 1K are sequentially arranged from the upstream side in the moving direction of the transfer paper 100 as the transfer material (the direction in which the belt 60 travels along the arrow A in the drawing). ing. Each of the toner image forming units 1Y, 1M, 1C, and 1K includes photosensitive drums 11Y, 11M, 11C, and 11K as image carriers and a developing unit. The arrangement of the toner image forming units 1Y, 1M, 1C, and 1K is set so that the rotation axes of the photosensitive drums are parallel to each other and arranged at a predetermined pitch in the transfer paper moving direction.

  In addition to the toner image forming units 1Y, 1M, 1C, and 1K, the laser printer includes an optical writing unit 2, paper feed cassettes 3 and 4, a registration roller pair 5, a transfer conveyance unit 6 as a transfer conveyance device, and belt fixing. A fixing unit 7 of a system, a paper discharge tray 8 and the like are provided. The transfer conveyance unit 6 has an endless transfer conveyance belt 60 as a transfer conveyance member that carries the transfer paper 100 and conveys the transfer paper 100 so as to pass through the transfer position of each toner image forming unit. In addition, the laser printer includes a manual feed tray MF and a toner supply container TC, and a waste toner bottle, a duplex / reversing unit, a power supply unit, and the like (not shown) are also provided in a space S indicated by a two-dot chain line.

  The optical writing unit 2 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each of the photosensitive drums 11Y, 11M, 11C, and 11K while scanning the laser beam based on image data. To do.

FIG. 2 is an enlarged view showing a schematic configuration of the transfer conveyance unit 6. The transfer conveyance belt 60 used in the transfer conveyance unit 6 is a high-resistance endless single-layer belt having a volume resistivity of 10 ⁹ to 10 ¹¹ Ωcm and a surface resistivity of 10 ¹² to 10 ¹⁴ Ω / □. The material is PVDF (polyvinylidene fluoride). The transfer / conveying belt 60 is wound around support rollers 61 to 68 so as to pass through transfer positions that are in contact with and face the photosensitive drums 11Y, 11M, 11C, and 11K of the toner image forming units.

  Outer peripheral surface of the transfer / conveying belt 60 so that the electrostatic suction roller 80 for conveying the transfer material to which a predetermined voltage is applied from the power source 80a faces the inlet roller 61 on the upstream side in the transfer paper moving direction among these supporting rollers. Is arranged. The transfer paper 100 that has passed between the two rollers 61 and 80 is carried on the transfer conveyance belt 60 by electrostatic attraction. A roller 63 is a drive roller that frictionally drives the transfer conveyance belt 60, and is connected to a drive source (not shown) and rotates in the direction of the arrow.

  The roller in the vicinity of the fixing unit 7 is thermally expanded by the heat of the fixing unit, and the roller diameter changes. In order to frictionally drive the transfer / conveying belt, the surface of the driving roller is formed of a rubber member such as silicone rubber having a high friction coefficient. Since a rubber member such as silicone rubber has a larger thermal expansion than a metal or the like, when the roller in the vicinity of the fixing unit 7 is a driving roller, the roller diameter is greatly changed. Normally, the speed of the transfer / conveying belt is controlled by the number of rotations of the driving roller. Therefore, when the diameter of the driving roller changes, the speed of the transfer / conveying belt changes. As a result, color shift may occur in the transferred image. Therefore, in this embodiment, the driving roller 63 is provided at a position away from the fixing unit 7. As a result, the driving roller 63 is not affected by the heat of the fixing unit, so that the diameter of the driving roller does not change. As a result, there is no change in the speed of the transfer / conveying belt, so that the color shift of the image can be suppressed.

  Transfer bias applying members 67Y, 67M, 67C, and 67K are provided at positions facing the photosensitive drum so as to be in contact with the back surface of the transfer conveyance belt 60 as transfer electric field forming means for forming a transfer electric field at each transfer position. Yes. These are bias rollers provided with a sponge or the like on the outer periphery, and a transfer bias is applied to the roller core from each transfer bias power source 9Y, 9M, 9C, 9K. Transfer charges are applied to the transfer conveyance belt 60 by the action of the applied transfer bias, and a transfer electric field having a predetermined strength is formed between the transfer conveyance belt 60 and the surface of the photosensitive drum at each transfer position. In addition, a backup roller 68 is provided to keep the contact between the transfer paper and the photoconductor in the area where the transfer is performed, and to obtain the best transfer nip.

The transfer bias applying members 67Y, 67M, and 67C and the backup roller 68 disposed in the vicinity thereof are integrally held by the swing bracket 93 so as to be rotatable, and can be rotated around a rotation shaft 94. This rotation is clockwise when the cam 96 fixed to the cam shaft 97 is rotated in the direction of the arrow.
The entrance roller 61 and the electrostatic adsorption roller 80 are integrally supported by the entrance roller bracket 90, and can be rotated clockwise from the state of FIG. A hole 95 provided in the swing bracket 93 and a pin 92 fixed to the entrance roller bracket 90 are engaged with each other, and rotate in conjunction with the rotation of the swing bracket 93. By the clockwise rotation of these brackets 90, 93, the bias applying members 67Y, 67M, 67C and the backup roller 68 disposed in the vicinity thereof are separated from the photoconductors 11Y, 11M, 11C, and the entrance roller 61 is electrostatically charged. The suction roller 80 also moves downward. It is possible to avoid contact between the photosensitive drums 11Y, 11M, and 11C and the transfer conveyance belt 60 in the monochrome mode in which an image of only black is formed.
As described above, the contact / separation means for contacting / separating the upstream portion of the transfer transport belt 60 in the transfer sheet transport direction with respect to the photosensitive drums 11Y, 11M, 11C is the swing bracket 93, the cam 96, and the entrance roller bracket 90. Etc.

  On the other hand, the transfer bias applying member 67K and the backup roller 68 adjacent to the transfer bias applying member 67K are rotatably supported by the outlet bracket 98, and are rotatable about a shaft 99 coaxial with the separation roller 62. When the transfer / conveyance unit 6 is attached to or detached from the main body, the transfer bias applying member 67K and the backup roller 68 adjacent thereto are rotated from the black image forming photosensitive member 11K by rotating clockwise by operating a handle (not shown). Are separated from each other.

  The separation roller 62 is applied with a separation bias having a polarity opposite to the toner polarity from a separation bias power source 62a. Due to the action of the separation bias, the toner on the transfer paper can be prevented from scattering when the transfer paper 100 is separated from the transfer conveyance belt 60. When the toner has a negative polarity, the voltage applied to the separation roller 62 is +2 kV. For the purpose of preventing toner scattering, the applied bias only needs to be applied when the toner image comes to the separation roller 62. However, in this embodiment, in order to simplify the control, it is always applied during transfer driving.

  A cleaning device 85 composed of a brush roller and a cleaning blade is disposed on the outer peripheral surface of the transfer conveyance belt 60 wound around the driving roller 63. The cleaning device 85 removes foreign matters such as toner adhering to the transfer conveyance belt 60. Further, a roller 64 is provided downstream of the driving roller 63 in the traveling direction of the transfer conveyance belt 60 in a direction for pushing the outer peripheral surface of the transfer conveyance belt, and a winding angle around the drive roller 63 is ensured. A tension roller 65 that applies tension to the belt with a pressing member (spring) 69 is provided in the loop of the transfer conveyance belt 60 further downstream from the roller 64.

  The one-dot chain line in FIG. 1 shown above indicates the conveyance path of the transfer paper 100. The transfer paper 100 fed from the paper feed cassettes 3 and 4 or the manual feed tray MF is transported by transport rollers while being guided by a transport guide (not shown). Then, it is sent to a temporary stop position where the registration roller pair 5 is provided. The transfer paper 100 delivered at a predetermined timing by the registration roller pair 5 is carried on the transfer conveyance belt 60, conveyed toward the toner image forming portions 1Y, 1M, 1C, and 1K, and formed at the transfer positions. Passes through the transfer nip.

In the color mode for forming a full-color image, each toner image developed on each of the toner image forming units 1Y, 1M, 1C, and 1K on the photosensitive drums 11Y, 11M, 11C, and 11K is transferred to the transfer paper 100 at each transfer nip. Is superimposed. Then, the image is transferred onto the transfer paper 100 under the action of the transfer electric field and nip pressure. By this superposition transfer, a full-color toner image is formed on the transfer paper 100.
The surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K after the toner image transfer are cleaned by a cleaning device, and are further discharged to prepare for the formation of the next electrostatic latent image.
On the other hand, the transfer paper 100 on which the full-color toner image is formed is fixed in the first paper discharge direction B or the second in accordance with the rotation posture of the switching guide G after the full-color toner image is fixed by the fixing unit 7. In the paper discharge direction C. When the paper is discharged from the first paper discharge direction B onto the paper discharge tray 8, it is stacked in a so-called face-down state with the image surface down. On the other hand, when the paper is discharged in the second paper discharge direction C, it is conveyed toward another post-processing device (such as a sorter or a binding device) (not shown), or is registered again for double-sided printing via a switchback unit. It is conveyed to the roller pair 5.

  Next, the characteristic part of this embodiment is demonstrated. When the transfer paper 100 is separated from the transfer conveyance belt 60, a bias having a polarity opposite to that of the toner is applied to the separation roller 62 of the transfer unit from the power source 62a in order to suppress image deterioration due to toner scattering. Thereby, since the toner is electrostatically adsorbed on the transfer paper, the toner can be prevented from being scattered when the transfer paper is separated from the transfer conveyance belt. When the leading edge of the transfer paper reaches the separation roller, a part of the transfer paper is still at the K-color transfer position next to the separation roller 62, and the toner image of the K-color photoconductor 11K is transferred to the transfer paper. .

  When the transfer paper gets wet in a high humidity environment, the resistance becomes low. FIG. 3 is a graph showing the relationship between the moisture content [%] and the surface resistivity [Ω / □] of the transfer paper. It can be seen that as the moisture content [%] increases for all four different transfer papers used in the experiment, the surface resistivity [Ω / □] decreases. Moreover, it turns out that the moisture content of a transfer paper rises as it becomes a high humidity environment. It can be seen that the surface resistivity of the transfer paper when the humidity is 54% or more is lower by about two orders of magnitude or more than the surface resistivity of the transfer paper when the humidity is 30% or less. In addition, when the moisture content of the transfer paper is 3% or less, there is not much difference in the surface resistivity of the transfer paper, but when the moisture content of the transfer paper exceeds 3.5%, the surface resistivity suddenly increases. You can see that it drops.

  As described above, when the transfer paper is damp in a high humidity environment and the resistance becomes low, the current flowing through the separation roller 62 flows into the K color transfer position through the transfer paper. As a result, the transfer current flowing through the K color transfer position becomes an overcurrent, and the polarity of some of the toner is reversed, and an abnormal image such as density unevenness may occur without being electrostatically attracted to the transfer paper. However, in this embodiment, the current limiter A of the separation bias power source 62a that applies the separation bias to the separation roller 62 is set to a value lower than the current flowing through the transfer bias application member 67K. Thereby, the transfer current is suppressed from being overcurrent, and the occurrence of abnormal images such as density unevenness can be suppressed.

  FIG. 4 is a graph showing the relationship between the transfer current and the transfer rate. When the transfer rate was 90% or more, a good image was obtained, but when the transfer rate was 90% or less, density unevenness was at a level where it could be visually confirmed. Accordingly, the sum of the current from the transfer bias applying member 67K and the current from the separation roller 62 flowing in from the transfer paper is within the current value range (hereinafter referred to as transfer current) at which a transfer rate of 90% or more shown in FIG. It can be seen that a good image can be obtained even in a high humidity environment. Usually, the current from the bias applying member 67K (hereinafter referred to as a transfer current set value) is set to approximately the center value of the transfer current set value width of the transfer current that achieves a transfer rate of 90% or more. Specifically, as shown in FIG. 4, the transfer current set value is set to 15 μA, which is approximately the center value of the transfer current set value width 12 μA to 21 μA of the transfer current. Therefore, the current limiter A of the separation bias power source 62a is set to ½ or less of the value (9 μA) obtained by subtracting the lower limit value (12 μA) from the upper limit value (21 μA) of the transfer current set value width. That is, the current limiter A of the separation bias power supply 62a is set to 4.5 μA or less. As a result, the sum of the current (4.5 μA) in which the current from the separation roller flows into the K color transfer position through the wet transfer paper and the transfer current set value (15 μA) is 19 μA. Further, the transfer current can be made to be not more than the upper limit (21 μA) of the transfer current that achieves a transfer rate of 90% or more. As a result, the transfer current does not become an overcurrent, and image deterioration such as density unevenness does not occur. Furthermore, if the current limiter A of the separation bias power supply 62a is set to 1 μA or less, it is possible to more reliably suppress the transfer current from becoming an overcurrent.

In this embodiment, a toner image having a predetermined pattern is directly formed on the transfer conveyance belt 60, and this toner image is detected by the adhesion amount sensor 70. Based on the detection result, image forming conditions such as charging conditions, exposure conditions, and development conditions are controlled.
An adhesion amount sensor 70 including a light emitting element and a light receiving element is provided at a position facing the separation roller 62. The transfer conveyance belt 60 is transparent or translucent. The separation roller 62 is a metal roller, and functions as a reflection plate that reflects light from the light emitting element of the adhesion amount sensor.
First, as shown in FIG. 5, toner images having M, Y, C, and B reference patterns are formed on the transfer conveyance belt 60. The light emitted from the light emitting element of the adhesion amount sensor 70 is regularly reflected and irregularly reflected by the separation roller 62 at the detection position. Either or both of the regularly reflected light and the irregularly reflected light are detected by the light receiving element of the adhesion amount sensor 70, and the toner adhesion amount is detected based on the light quantity. When the reference pattern formed on the transfer / conveying belt passes through the detection position, the light transmittance of the toner layer decreases as the toner amount increases. For this reason, the amount of light that passes through the transfer conveyance belt 60 from the light emitting element of the adhesion amount sensor and is applied to the separation roller 62 and the amount of reflected light from the separation roller 62 are reduced. On the other hand, when no toner is present on the transfer conveyance belt 60, light emitted from the light emitting element of the adhesion amount sensor 70 passes through the transfer conveyance belt 60 and is irradiated to the separation roller 62. The light is reflected by a metal separation roller 62 having a high reflection efficiency, and reflected light having a high light intensity is input to the light receiving element of the adhesion amount sensor 70. For this reason, when no toner is present on the transfer conveyance belt 60, the output of the adhesion amount sensor 70 becomes high. As a result, the difference in the output of the adhesion amount sensor 70 increases when there is no toner on the transfer conveyance belt 60 and when there is toner. For this reason, a high S / N ratio can be obtained, and the detection ability of the toner adhesion amount can be improved. Further, by using the reflective adhesion amount sensor 70, the light emitting element and the light receiving element can be supported by a single support member, and the assembling work for determining the relative position with respect to the separation roller 62 is also a transmissive adhesion amount. It can be performed more easily than a sensor.

  Then, after detecting the toner image on the transfer conveyance belt 60, the toner image on the transfer conveyance belt 60 is removed by a cleaning device (not shown). On the other hand, normal image printing is executed by controlling the image forming conditions for each color according to the adhesion amount detection result.

  The toner adhesion amount detection means can be used not only to control the image forming conditions by detecting the toner amount of each color, but also as a misregistration detection sensor for detecting misregistration of the toner image of each color.

As described above, according to the image forming apparatus of the present embodiment, the current limiter A of the separation bias power source 62a that applies the separation bias to the separation roller 62 is set to a value lower than the transfer current. This suppresses the transfer current from becoming overcurrent even if the transfer paper gets damp in a high humidity environment and the resistance becomes low, and the current from the separation roller flows through the transfer paper to the K color transfer position. Is done. As a result, the occurrence of abnormal images such as density unevenness can be suppressed.
Further, according to the image forming apparatus of the present embodiment, the sum of the current from the transfer bias applying member 67K and the current of the current limiter A of the separation bias power supply 62a has a current value that can obtain a transfer rate of 90% or more. Within range. As a result, a transfer rate of 90% or more can be obtained even when the current from the separation bias power source 62a flows into the transfer position due to the transfer paper wet. As a result, an abnormal image such as density unevenness does not occur and a good image can be obtained.
Further, according to the image forming apparatus of the present embodiment, the current limiter A of the separation bias power source 62a is set to ½ or less of the transfer current set value width. As a result, a transfer rate of 90% or more can be obtained even when the current from the separation roller passes through the transfer paper and flows into the K color transfer position. As a result, an abnormal image such as density unevenness does not occur and a good image can be obtained.
Further, according to the image forming apparatus of the present embodiment, the current limiter A of the separation bias power source 62a is set to 1 μA or less. Thereby, it can suppress more reliably that a transfer current turns into an overcurrent. As a result, an abnormal image such as density unevenness does not occur and a good image can be obtained.
Further, according to the image forming apparatus of the present embodiment, the surface resistivity of the transfer conveyance belt 60 is set to 1E + 12 [Ω / □] or more. As a result, the surface of the transfer belt has a high resistance, and it is possible to suppress current from flowing from the separation bias power source 62a and each of the transfer bias power sources 9Y, 9M, 9C, and 9K to the other transfer positions through the surface of the transfer belt. it can. As a result, each transfer current becomes an overcurrent, and density unevenness does not occur.
Further, according to the image forming apparatus of this embodiment, the adhesion amount sensor 70 is disposed at a position facing the separation roller 62, and the position of the toner image of the reference pattern directly formed on the transfer conveyance belt 60 and the toner adhesion amount. Is detected. Based on the detection result, image forming conditions and the like are controlled. Thereby, the malfunction which arises at the time of image formation can be eliminated.
Further, according to the image forming apparatus of the present embodiment, the separation roller 62 is a metal roller having good reflectivity. As a result, reflected light having a high light intensity can be input to the light receiving element of the adhesion amount sensor 70. For this reason, when no toner is present on the transfer conveyance belt 60, the output of the adhesion amount sensor 70 becomes high. As a result, a high S / N ratio can be obtained, and the ability to detect the toner adhesion amount can be improved.
Further, according to the image forming apparatus of the present embodiment, the driving roller 63 is provided at a position away from the fixing unit 7. As a result, the driving roller 63 is not affected by the heat of the fixing unit, so that the diameter does not change due to thermal expansion. As a result, there is no change in the speed of the transfer / conveying belt, so that color misregistration of the image can be suppressed.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment. 1 is a schematic configuration diagram of an entire transfer conveyance unit of an image forming apparatus according to an embodiment. The figure which shows the relationship between the surface resistivity of a transfer paper, and a moisture content. The figure which shows the relationship between a transcription | transfer current and a transcription | transfer rate. FIG. 4 is a schematic diagram illustrating a reference pattern image formed on a transfer conveyance belt. (A) is a schematic diagram showing a current path from a separation roller when a transfer paper with moisture is conveyed, and (b) is a separation roller when a transfer paper without moisture is conveyed. The schematic diagram which shows the electric current path from.

Explanation of symbols

1Y, 1M, 1C, 1K Toner image forming section 5 Registration roller pair 6 Transfer conveyance unit 9Y, 9M, 9C, 9K Transfer bias power supply 11Y, 11M, 11C, 11K Photosensitive drum 60 Transfer conveyance belt 62 Separation roller 62a Separation bias power supply 67Y, 67M, 67C, 67K Transfer bias applying member 80 Electrostatic adsorption roller

Claims (7)

A plurality of image carriers that carry toner images charged to a predetermined polarity;
An endless transfer material conveyance belt for conveying the transfer material to the toner image on these image bearing member sequentially passes through the plurality of transfer position to be transferred,
A plurality of stretching rollers that are in contact with the back surface of the transfer material transport belt and rotatably rotate the transfer material transport belt;
In an image forming apparatus provided with a plurality of transfer bias applying members arranged at each transfer position and applying a transfer bias from the back surface of the transfer material conveying member at the transfer position,
The transfer material conveyance belt has a surface resistivity of 1E + 12 [Ω / □] or more,
In order to suppress toner scattering when the transfer material is separated from the transfer conveyance belt , a separation roller which is a tension roller located at a position where the transfer material is separated from the transfer material conveyance belt among the plurality of tension rollers. A separation bias power source for applying a separation bias having a polarity opposite to the charging polarity of the toner image;
An image forming apparatus comprising a current limiter for limiting a current flowing through the separation roller so that a current value flowing through the separation roller is smaller than a current value flowing through the transfer bias applying member. The image forming apparatus according to claim 1.
An image forming apparatus, wherein a transfer rate at which a toner image on an image carrier is transferred to a transfer material is 90% or more. The image forming apparatus according to claim 2.
The difference between the upper limit value and the lower limit value of the range of transfer current that flows to the transfer position where the transfer rate at which the toner image on the image carrier is transferred to the transfer material is 90% or more is the current value that flows to the separation roller. An image forming apparatus, wherein the current limiter is set so as to be limited to ½ or less of the value. The image forming apparatus according to claim 2.
In the current limiter, the sum of the current value flowing through the separation roller and the current value flowing through the transfer bias applying member is such that the transfer rate at which the toner image on the image carrier is transferred to the transfer material is 90% or more. An image forming apparatus, wherein the current flowing through the separation roller is limited to be equal to or less than an upper limit value of a range of a transfer current value flowing through the transfer position. The image forming apparatus according to claim 1, 2, 3, or 4.
An image forming apparatus, wherein the current limiter is set so that a current value flowing through the separation roller is 1 μA or less . The image forming apparatus 請 Motomeko 1, 2, 3, 4 or 5,
An image forming apparatus comprising: a detecting portion formed on the transfer material conveying belt; and a detecting means for detecting the detecting portion. The image forming apparatus according to claim 1, 2, 3, 4, 5 or 6 .
The partial release roller, together with a metal roller, the drive roller for rotationally driving the transfer material conveyance belt, the image forming apparatus, characterized in that is other than the separation roller.

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