JP2002040816A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the tailing of unfixed toner at the time of fixing, image rubbing or the staining of an edge caused by the spring of a trailing edge. SOLUTION: In order to separate recording material to which a toner image on a photoreceptor drum is transferred from the photoreceptor drum, a destaticizing needle bias is applied to a destaticizing needle. By providing -1.2 kV and -2.5 kV as the potential level of the destaticizing needle bias applied to the destaticizing needle, the potential level is set to -1.2 kV for the first surface of the recording material, and set to -2.5 kV at the leading edge and the trailing edge of the second surface thereof and -1.2 kV at a middle part between the leading edge and the trailing edge for the second surface when humidity detected by an environment sensor is >=70%. By controlling in such a way, the occurrence of the tailing of the first surface, the image rubbing or the staining of the edge caused by the spring of the trailing edge of the first surface, the separation defect of the leading edge of the second surface, the sticking of the recording material to a carrying guide and the spring of the trailing edge of the second surface under environment where the humidity is >=70% are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.

[0002]

2. Description of the Related Art An image forming apparatus of a type in which a toner image is formed on a photosensitive drum as an image carrier and the toner image is transferred onto a recording material such as paper by a transfer roller to which a transfer bias is applied, for example, a copying machine Machines, printers, facsimile machines and the like are known.

In such an image forming apparatus, the recording material on which the transfer of the toner image has been completed is electrostatically attracted to the surface of the photosensitive drum. The edges may be charged to the same polarity as the transfer bias by peeling charging, and the separation of the trailing edge of the recording material from the photosensitive drum may be delayed.

If the separation of the trailing edge of the recording material from the photosensitive drum is delayed, the trailing edge of the recording material is pulled in the direction in which the photosensitive drum rotates, and jumps up so that the trailing edge of the recording material approaches the photosensitive drum. Rear end bouncing occurs. And
Due to this rear end bouncing, the rear end of the recording material comes into contact with the bottom of the cleaning container, and the unfixed toner image on the recording material is disturbed and the image is rubbed, or toner adheres to the bottom of the cleaning container and subsequent recording is performed. It transfers to the recording material, and the edge of the recording material at the rear end is stained.

In the case where double-sided image formation (double-sided printing) is performed, when the second side (second side) image is formed, the recording material curled in the same direction as the curvature of the photosensitive drum after the first side image formation is completed. As a result, the effect of curvature separation is reduced, and the leading end of the recording material cannot be separated from the photosensitive drum, thereby causing a problem that a paper jam occurs.

Therefore, a predetermined potential is applied to the static elimination needle to eliminate the charge of the recording material to promote separation from the photosensitive drum. The sequence at this time is shown in FIG. By applying -2.5 kV to the vicinity of the rear end of the recording material on both the first surface and the second surface of the recording material and removing the electric charge, image defects such as image rubbing and contamination due to the rear end of the recording material can be prevented. Similarly, the leading end of the second side of the recording material is also -2.5 k.
By applying V to eliminate the charge, the recording material curled in the same direction as the photosensitive drum can be separated from the photosensitive drum at the tip of the second surface of the recording material. Further, a static elimination needle bias of -1.2 kV is also applied to the central portion of the recording material to prevent conveyance failure due to electrostatic attraction to the conveyance guide.

[0007]

However, in the above-mentioned prior art, the following problems occur depending on the use environment of the image forming apparatus.

In a high-humidity environment, the resistance of the recording material is reduced, so that the electric charge that originally should not be deposited on the recording material as transfer charge is lost, and the electrostatic force that keeps the toner on the recording material is eliminated. Becomes weaker. In such a state, at the time of fixing, the moisture contained in the recording material evaporates violently, and the unfixed toner on the recording material may be fixed in a state of being scattered in a direction opposite to the paper transport direction. This is called tailing, and an image as shown in FIG. 10 is formed. This figure shows an image defect that occurs when a horizontal line image having a width of 100 μm is formed in a direction perpendicular to the paper conveyance direction, that is, a tailing. When using a hygroscopic paper (paper with a high water content) in a high humidity environment, if a bias having a polarity opposite to that of the transfer bias is applied to the static elimination needle at the rear end of the recording material, the resistance of the recording material is low. The electric charge of the unfixed toner image on the upper side is removed, and FIG.
As shown in (1), tailing sometimes occurred over a wide range of the rear end of the first surface of the recording material. The length D of the trailing range in the paper transport direction is substantially equal to the distance between static elimination and fixing.

On the other hand, in a low-humidity environment, when the recording material is thin and stiff (weak), or when the outer diameter of the photosensitive drum is large, the separating action from the photosensitive drum due to the stiffness of the recording material (curvature separation) cannot be expected. However, there is a problem that the leading end of the first surface cannot be separated from the photosensitive drum and a paper jam occurs. For example, when a thin paper having a basis weight (weight per unit area) of 60 g / m ² or less is used as the recording material, or when the outer diameter of the photosensitive drum is 40 mm or more, paper jam tends to occur.

In a low humidity environment where such a recording material is easily charged, calcium carbonate (CaCO 3) is used as a filler.
_{When a} large number of recording materials containing 10% or more of ₃ ) are passed, positively charged calcium carbonate powder is electrically attracted to the surface of the fixing roller which has a negative potential for the purpose of preventing offset. As a result, the fixing bias is canceled, and the unfixed toner on the recording material is electrically offset to the surface of the fixing roller. Furthermore, the offset deteriorates because the releasability of the surface of the fixing roller decreases due to the adhesion of the calcium carbonate powder. The offset toner is transferred from the surface of the fixing roller to the surface of the pressure roller due to a difference in releasability at a conveyance interval between the preceding recording material and the succeeding recording material (hereinafter, referred to as “paper interval”). Accumulates on the surface. In such a process, the toner adhering and accumulating on the pressure roller causes stain on the back surface of the recording material and returns to the fixing roller again to cause stain on the surface of the recording material.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it has been found that tailing of unfixed toner, paper jam due to poor separation of the recording material, toner contamination of the recording material due to calcium carbonate in the recording material, and the like are provided. It is an object of the present invention to provide an image forming apparatus capable of preventing such a situation.

[0012]

According to the first aspect of the present invention, a voltage having a polarity opposite to the polarity of a toner image formed on an image carrier is applied from the back surface of a recording material. Transfer means for transferring the toner image on the image carrier to the surface of the recording material, a static elimination member for neutralizing the recording material after toner image transfer and separating the recording material from the image carrier surface, and An image forming apparatus comprising: a static elimination power supply for applying a static elimination bias; and control means for changing a potential level of the static elimination bias applied to the static elimination member by the static elimination power supply, wherein at least one of an ambient temperature and humidity is included. Wherein the control means changes a potential level of a charge removing bias applied to the charge removing member by the charge removing power supply based on a detection result of the environment detecting means. To.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus further includes a double-sided mode for forming an image on the first side of the recording material and then forming an image on the second side of the recording material. When the double-sided mode is selected and at least one of the temperature and humidity detected by the environment detection unit is equal to or more than a predetermined value, the control unit performs the image formation when forming an image on the first surface of the recording material. The potential level applied to the charge removing member is set to be smaller than the trailing end of the recording material in the transport direction.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the predetermined value for the humidity is 70% relative humidity.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus further includes a double-side mode in which an image is formed on a first side of the recording material and then an image is formed on a second side of the recording material. When the double-sided mode is selected and at least one of the temperature and the humidity detected by the environment detecting unit is equal to or less than a predetermined value, the control unit forms an image on the first and second surfaces of the recording material. The potential level applied to the charge removing member with respect to the recording material at that time is set to be large.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the predetermined value for the humidity is a relative humidity of 20%.

According to a sixth aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus has a plurality of modes in which a process condition can be changed by a user arbitrarily selecting a mode. When at least one mode is set, the control unit sets the potential level to be applied to the charge eliminating member with respect to the leading end in the transport direction of the recording material when forming an image on the first surface of the recording material. It is set to be large.

According to a seventh aspect of the present invention, there is provided the image forming apparatus according to the first aspect, further comprising a double-side mode in which an image is formed on the first side of the recording material and then an image is formed on the second side of the recording material. Has a plurality of modes in which the process conditions can be changed by arbitrarily selecting a mode. When at least one of the modes is set, the control unit controls the first surface of the recording material. And setting the potential level to be applied to the static elimination member to be large with respect to the recording material when forming an image on the second surface.

[Operation] According to the above-described configuration, an appropriate charge removing bias can be applied to the charge removing member in accordance with the temperature, humidity, and process conditions, so that image defects such as tailing can be prevented. it can.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> FIG. 1 shows an example of an image forming apparatus according to the present invention. The image forming apparatus shown in FIG.
A laser beam printer having a double-sided mode capable of forming images on both front and back surfaces (first and second surfaces) of one recording material P, that is, after forming an image on the first surface, the recording material P is subjected to image formation. This is a laser beam printer capable of forming an image on the second surface thereof without discharging it to the outside of the forming apparatus main body, and FIG.

When forming an image on both the front and back surfaces of one recording material P by the above-described laser beam printer (hereinafter, referred to as an "image forming apparatus"), first, a plurality of recording materials P stored in a paper cassette 36 are stored. Recording material 19 (for example,
The paper is fed one by one from the paper) by the paper feed roller 25, and is transported along the guide 34 to the transport roller pair 33. Recording material 19
Is further transported by the rotation of the transport roller pair 33, and is transported along the guide 32 to the registration roller pair 31.
The registration roller pair 31 rotates in accordance with the toner image formed on the photosensitive drum 1 to transfer the recording material 19 to the transfer guide 1.
4 to the transfer nip N.

An image is formed on the photosensitive drum 1 as follows. First, the photosensitive drum 1 is uniformly charged to a predetermined polarity and a predetermined potential by the primary charger 29, and then the exposure device 2
Exposure is performed by 8 to form an electrostatic latent image.

Toner is adhered to the electrostatic latent image by a developing device 30 and developed as a toner image. This toner image is electrostatically transferred to the surface (first surface) of the recording material 19 supplied to the transfer nip N by applying a transfer bias having a polarity opposite to that of the toner to the transfer roller (transfer means) 4. You.

The recording material 19 after the transfer of the toner image is conveyed to the fixing device 13 along the pre-fixing guide 10, where it is heated and pressed to fix the toner image on the surface (first surface).
After the transfer of the toner image, the toner remaining on the surface of the photosensitive drum 1 that has not been transferred to the recording material 19 (transfer residual toner) is removed by the cleaning device 12 and used for the next image formation.

Recording material 19 having a toner image fixed on its surface
Is discharged from the fixing device 13 and swings freely.
7 is located at the upper position (the position indicated by the broken line), and is conveyed along the lower guide 39 and reaches the reversing roller 40. The leading end of the recording material 19 is moved along the guide 41 by the normal rotation of the reversing roller 40. Reversing roller 40
Is switched from normal rotation to reverse rotation when the rear end of the recording material 19 arrives, whereby the recording material 19 is transported along the guide 42 to the transport roller pair 43. Transport roller 43
Transports the recording material 19 along the guide 44 to the transport roller pair 33
The recording material 19 is again transferred to the same transfer step as the first side,
Then, the toner image is fixed on the second surface.

The recording material 19 on which the second surface has been fixed is conveyed along the upper guide 38 by the flapper 37 being disposed at the lower position (the position indicated by the solid line). It is discharged onto 46. FIG.
Numeral 47 denotes a housing constituting the image forming apparatus main body.

FIG. 2 is an enlarged view in which a part of FIG. 1 is enlarged to show the features of the present embodiment, that is, an enlarged vertical sectional view near the transfer portion. In FIG. 2, the same members as those in FIG. 1 are denoted by the same reference numerals.

As shown in FIG. 1, the image forming apparatus according to the present embodiment includes a drum-type electrophotographic photosensitive member (hereinafter, referred to as "photosensitive drum") 1 as an image carrier.
In the present embodiment, the photosensitive drum 1 is a photosensitive drum provided with an organic photosensitive member (OPC) layer on the surface of an aluminum cylinder, and has an outer diameter of 30 mm. The photosensitive drum 1 is
It is rotationally driven at a predetermined process speed (peripheral speed) in the direction of arrow R1 by a driving means (not shown).

The surface of the photosensitive drum 1 has a charger 29.
After being uniformly charged to a negative polarity by (see FIG. 1), image exposure is performed by an exposure device 28 (see FIG. 1) to form an electrostatic latent image on the surface. This electrostatic latent image is reversely developed by the developing device 30 (see FIG. 1). That is, the photosensitive drum 1
The upper electrostatic latent image is developed as a toner image by attaching negative polarity toner.

The toner image on the photosensitive drum 1 is transferred to a recording material 19 conveyed along a transfer guide 14 by a transfer roller (transfer means) 4. The transfer roller 4
This is a roller-shaped member having an outer diameter of 20 mm, which is configured by providing a conductive elastic layer 2 on a metal core 3. The transfer roller 4 is pressed by the photosensitive drum 1 to form a transfer nip N between the transfer roller 4 and the photosensitive drum 1. The transfer roller 4 transfers the toner image on the photosensitive drum 1 to the recording material 19 conveyed to the transfer nip N by applying a positive voltage having a polarity opposite to the charging polarity of the toner image by the transfer high-voltage power supply 5. Transfer to

The volume resistivity of the elastic layer 2 of the transfer roller 4 is about 2 × 10 ⁸ Ω · cm in an environment of a temperature of 20 ° C. and a humidity of 60% (relative humidity Rh). The transfer bias applied to No. 3 is about 0 V to +6 kV. The voltage applied to the transfer roller 4 is controlled by changing its magnitude depending on the resistance value of the transfer roller 4 or by switching its magnitude between during transfer, during non-transfer or when stopped. The control is performed by a control system having a CPU (control means) 15, an I / O port 16, a bus line 18, and a memory 17. This control system incorporates an environment sensor 26 as environment detection means.
In step 6, the transfer bias is controlled by detecting the temperature and humidity in the atmosphere.

The recording material 19 after the transfer of the toner image is electrostatically adsorbed on the surface of the photosensitive drum 1, and the recording material 19 is separated by the static elimination needle (static elimination member) 6. The static elimination needle 6 is 0.1 m thick
m stainless steel (SUS) plate,
As shown in FIG. 3, the tip 6a is formed in a pointed shape (saw blade shape). The static elimination needle 6 has, for example, a tip 6
The pitch a of a is 1 mm, and the height b of the peak is 2 mm.

As shown in FIG. 2, the static elimination needle 6 is sandwiched between insulating members 7, and together with the insulating member 7, constitutes a static elimination needle unit 8. The recording material 19 onto which the toner image has been transferred and further separated from the photosensitive drum 1 is conveyed on a conveyance guide 10 made of an insulating resin and conveyed to the fixing device 13.

The fixing device 13 includes a fixing roller 20 having a cylindrical aluminum core coated with PFA (perfluoroalkoxy), a halogen heater 21 for warming the fixing roller 20 from the inside, and a recording roller 19 for fixing the recording material 19 to the fixing roller 20. The pressure roller 22 and the recording material 19 are pressed against
And a fixing entrance guide 23 for guiding to a fixing nip portion between the pressure roller 22 and the pressure roller 22. Recording material 19 after transfer
Is passed through the fixing nip to form the surface (1).
The toner image is fixed on the surface. The toner remaining on the photosensitive drum 1 without being transferred to the recording material 19 in the transfer process is collected by the cleaning device 12. The cleaning device 12 has a cleaning blade 24 for scraping off transfer residual toner from the surface of the photosensitive drum 1 and a cleaning container 25 for storing waste toner.

In the present embodiment, a high-voltage power supply (static power supply) 9 applies a neutralization needle bias (static bias) to the static elimination needle 6 so that the leading end of the second surface of the recording material 19 can be satisfactorily separated. , And the rear end is prevented from sticking to the conveyance guide 10. Furthermore, the present embodiment is characterized in that the static elimination needle bias control is switched by the CPU 15 in accordance with the environment determined by the environment sensor 26.

FIG. 6 shows a sequence when the environment sensor 26 detects a humidity of 70% or more. In a high humidity environment of 70% or more, a large transfer bias is not applied to the static elimination needle 6 at the rear end of the first surface where the recording material 19 is absorbing moisture. As a result, it is possible to prevent the charge between the fixing and discharging needles from being discharged, and to prevent the occurrence of tailing of an extremely low level of a hundred and several tens mm on the rear end side. In a high-humidity environment, since the resistance of the recording material 19 is reduced, the charging is small and the separation from the photosensitive drum 1 is not delayed, and the rear end bouncing hardly occurs. Therefore, even if a large transfer bias (-2.5 kV) is not applied as a potential level, problems such as image rubbing and edge contamination do not occur. In addition, recording material 1
By applying -2.5 kV to the tip of the second surface of No. 9, the recording material 19 is well separated from the photosensitive drum 1, and a small transfer bias of -1.2 kV is applied as a potential level to the center. This prevents sticking to the transport guide 10, and prevents rear end bouncing by applying -2.5 kV to the rear end of the second surface. In this manner, the sheet passing performance of the second side of the recording material 19 can be improved.

That is, in the present embodiment, the potential level of the static elimination needle bias applied to the static elimination needle 6 is-
When 1.2 kV and -2.5 kV are provided, and the humidity detected by the environment sensor 26 is 70% or more, one of the recording materials 19
For the surface, the potential level is -1.2 kV, for the second surface, -2.5 kV at the front and rear ends, and -1.2 kV at the intermediate portion between the front and rear ends. By switching the potential level of the static elimination needle bias at such an application timing, tailing occurs on the first surface in an environment where the humidity is 70% or more, image rubbing and edge contamination due to the rear end jumping of the rear end of the first surface, and the like. The separation failure at the front end of the second surface and the sticking of the recording material 19 to the conveyance guide 10 prevent the rear end of the second surface from jumping.

<Embodiment 2> In this embodiment, an example in which the static elimination needle bias control is switched in a low humidity environment will be described.

FIG. 7 shows a sequence when the environment sensor 26 detects a humidity of 20% or less. In a low-humidity environment of 20% or less, both the first and second surfaces of the recording material 19 have a large neutralization needle bias (−2.5 kV) from the leading end to the trailing end by the neutralizing needle high voltage power supply 9 with respect to the neutralizing needle 6. Is applied. In a low-humidity environment, since the recording material 19 is dry and has a high resistance, the recording material 19 is hard to be neutralized and does not have a poor level of tailing. Further, the entire recording material is largely negatively charged to prevent the calcium carbonate powder from being positively charged when the recording material 19 is passed through calcium carbonate paper. Accordingly, it is possible to prevent the calcium carbonate powder from electrically adhering to the surface of the fixing roller, which is a negative potential at which the pressure roller stains start. Similarly, on the second side, a large bias of the static elimination needle was applied to the static elimination needle from the front end to the rear end of the recording material 19 to take a countermeasure against pressure roller contamination.

<Embodiment 3> In this embodiment, a case will be described in which an image is formed (printed) on weakly stiff paper such as thin paper in a low temperature or low humidity environment. FIG. 4 is a longitudinal sectional view of the vicinity of the transfer section of the image forming apparatus according to the present embodiment.
4, the same members as those in FIG. 2 of the first embodiment are denoted by the same reference numerals, and redundant description will be omitted as appropriate.
A description of the same parts as in the first embodiment will be omitted.

The conveyance guide 10A disposed between the transfer roller 4 and the fixing device 13 is provided with a comb-shaped insulating resin rib 2 having a portion in contact with the back surface of the recording material 19.
By providing an electrically grounded sheet metal 11 for absorbing the recording material between the ribs 27, the paper is conveyed by lift due to curling of the recording material 19 and resistance to air. Prevent instability.

The image forming apparatus shown in FIG. 4 has a special paper mode. A switch (not shown) for setting special paper is provided on the operator operation panel 35, and when the user selects an appropriate mode with this switch, the transport of the recording material 19 is performed according to the type of the recording material 19. Process conditions such as speed and fixing temperature can be partially changed. For example, a recording material 19 having a basis weight of 65 g / m ² or less
Recommends users to set to thin paper mode. In an apparatus having such a special paper mode,
The bias control of the static elimination needle of the static elimination needle 6 is switched in combination with the special paper setting.

FIG. 8 shows a sequence when the environment sensor 26 detects a temperature of 15 ° C. or less or a humidity of 10% or less and the thin paper setting is set. When thin paper is passed as the recording material 19 in a low-temperature environment of 15 ° C. or less or a low-humidity environment of 10% or less, the discharge needle high-voltage power supply 9 provides a large -2.5 kV with respect to the discharge needle 6 even at the leading end of the first surface. Apply a potential level. Thereby, the effect of electrostatic separation at the front end of the first surface by the static elimination needle 6 can be increased, so that paper jam of thin paper in a low-temperature or low-humidity environment can be prevented. In addition, -2.5 kV at the tip of the second side
Is applied, the thin paper can be satisfactorily separated from the photosensitive drum 1. Also, from a little behind the leading end of the thin paper to just before the trailing end, -1.2 kV is applied to prevent electrostatic attraction to the transport guide to prevent paper jam due to sticking. By applying 2.5 kV, rear end bouncing was prevented.

<Embodiment 4> In this embodiment, a case where an image is formed on calcium carbonate paper as the recording material 19 in a low humidity environment will be described. In the apparatus having the special paper setting shown in FIG. 4, for example, for a paper mainly used in Europe and containing 10% or more of calcium carbonate as a filler, the user is recommended to set the calcium carbonate paper mode. .

FIG. 9 shows a sequence when the environment sensor detects a humidity of 20% or less and the paper is set to the calcium carbonate paper. In a low humidity environment of 20% or less,
When passing the calcium carbonate paper, a large bias (−2.5 kV) is applied to the static elimination needle 6 from the leading end to the rear end of the calcium carbonate paper by the static elimination needle high voltage power supply 9. In low humidity environment, calcium carbonate paper is dry,
Due to the high resistance, the calcium carbonate paper is hard to be neutralized, and does not cause poor level tailing. Further, the entire calcium carbonate paper is largely negatively charged to prevent the calcium carbonate powder from being positively charged when the calcium carbonate paper is passed. Accordingly, it is possible to prevent the calcium carbonate powder from electrically adhering to the surface of the fixing roller, which is a negative potential at which the pressure roller stains start. Similarly, on the second side, a large bias was applied to the static elimination needle 6 from the leading end to the trailing end of the paper to take a countermeasure against pressure roller contamination.

In the above-described second embodiment, in the case of a low-humidity environment, the sequence of voltage applied to the static elimination needle is as shown in FIG. 7 (FIG. 9). In the present embodiment, the environment sensor 26 determines that the environment is a low-humidity environment. Further, it is characterized in that the static elimination needle bias control is switched only in the calcium carbonate paper mode.

In the first to fourth embodiments, the recording material 19
Although an example in which image formation is performed on both front and back surfaces has been described, the present invention can of course be applied to a case where an image is formed on one surface (for example, the first surface) of the recording material 19.

[0049]

As described above, according to the present invention,
By changing the potential level of the charge removing bias applied to the charge removing member by the charge removing power supply based on the temperature or humidity detected by the environment detecting means, the charge removal on the recording material can be made appropriate, so that the unfixed toner Tailing, paper jam due to poor separation of the recording material, toner contamination of the recording material due to calcium carbonate in the recording material, and the like can be prevented.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is an enlarged longitudinal sectional view showing the vicinity of a transfer portion according to the first embodiment.

FIG. 3 is a front view of a static elimination needle.

FIG. 4 is a longitudinal sectional view illustrating a schematic configuration of an image forming apparatus according to a second embodiment.

FIG. 5 is a view showing a potential level of a static elimination bias applied to a conventional static elimination needle.

FIG. 6 is a diagram showing a potential level of a discharging bias applied to a discharging needle according to the first embodiment.

FIG. 7 is a diagram showing a potential level of a discharging bias applied to a discharging needle according to the second embodiment.

FIG. 8 is a diagram showing a potential level of a discharging bias applied to a discharging needle according to a third embodiment.

FIG. 9 is a diagram showing a potential level of a discharging bias applied to a discharging needle according to a fourth embodiment.

FIG. 10 is a diagram illustrating a state in which tailing occurs.

FIG. 11 is a diagram illustrating a range in which tailing occurs.

[Explanation of symbols]

 Reference Signs List 1 image carrier (photosensitive drum) 4 transfer means (transfer roller) 6 static elimination member (static elimination needle) 15 control means (CPU) 19 recording material 26 environment detecting member (environment sensor)

Claims (7)

[Claims] A transfer means for applying a voltage having a polarity opposite to the polarity of the toner image formed on the image carrier from the back surface of the recording material to transfer the toner image on the image carrier to the surface of the recording material; A static elimination member that neutralizes the recording material after toner image transfer and separates the recording material from the surface of the image carrier; a static elimination power source that applies a static elimination bias to the static elimination member; and a static elimination bias that the static elimination power source applies to the static elimination member Control means for changing the potential level of the image forming apparatus, comprising: environment detection means for detecting at least one of the temperature and humidity of the atmosphere; and the control means detects a detection result of the environment detection means. An image forming apparatus configured to change a potential level of a charge removing bias applied to the charge removing member by the charge removing power source based on the following. 2. A two-sided mode for forming an image on the second side of the recording material after forming an image on the first side of the recording material, wherein the two-sided mode is selected, and the temperature, humidity, and temperature detected by the environment detecting means are provided. When at least one of them is equal to or more than a predetermined value, the control unit controls the potential applied to the charge removing member with respect to a rear end of the recording material in a conveying direction when forming an image on the first surface of the recording material. The image forming apparatus according to claim 1, wherein the level is set to be small. 3. The image forming apparatus according to claim 2, wherein the predetermined value of the humidity is 70% relative humidity. 4. A double-sided mode for forming an image on the second side of the recording material after forming an image on the first side of the recording material, wherein the double-sided mode is selected and the temperature, humidity, and temperature detected by the environment detecting means are provided. When at least one of them is equal to or less than a predetermined value, the control unit sets the potential level applied to the charge eliminating member to the recording material when forming an image on the first and second surfaces of the recording material. The image forming apparatus according to claim 1, wherein the setting is made larger. 5. The image forming apparatus according to claim 4, wherein the predetermined value of the humidity is a relative humidity of 20%. 6. An image forming apparatus having a plurality of modes in which process conditions can be changed, wherein a user can change a setting by arbitrarily selecting a mode, wherein at least one of the modes is selected. Wherein the control means sets the potential level to be applied to the charge eliminating member higher than the leading end in the transport direction of the recording material when forming an image on the first surface of the recording material. The image forming apparatus according to claim 1, wherein: 7. A double-sided mode for forming an image on a second side of the recording material after forming an image on a first side of the recording material,
It has multiple modes in which process conditions can be changed,
In an image forming apparatus in which a user can change a setting by arbitrarily selecting a mode, when at least one of the modes is set, the control unit controls the first and second surfaces of the recording material. 2. The image forming apparatus according to claim 1, wherein the potential level applied to the charge eliminating member is set higher than that of the recording material when forming an image on a surface.