JP2001194916A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device where a blurred transfer generated by charge of a reverse polarity with respect to toner T on a transfer surface of transfer paper 50 can be eliminated. SOLUTION: In the device, a conductive Mylar(R) 21 is installed as an electrode above a transfer surface guide part 1a so that it is made to face a back side guiding member 22 and brought into contact with the transfer paper 50 that is fed toward a transfer nip and a developing bias power source 14 to generate AC and DC superposed bias is connected to the conductive Mylar(R) 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile, and the like.
The present invention relates to an image forming apparatus that transfers a visible image on a visible image holding member to a transfer member.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus,
A device that forms an image by the following process is known. That is, after a latent image carrier such as a photoreceptor is uniformly charged, optical writing corresponding to an image signal is performed by a laser scanning optical system or an LED light writing optical system or the like, and an electrostatic charge is formed on the latent image carrier. Form a latent image. Next, after a toner as a developer is attached to the electrostatic latent image by a developing device to obtain a toner image, the toner is transferred to a transfer body which is conveyed to a transfer position which is a position facing the latent image carrier and the transfer means. Transfer the image. When a primary transfer body such as an intermediate transfer body is used as the transfer body, the toner image is retransferred from the primary transfer body to a secondary transfer body such as a sheet to obtain an image.

In such a series of image forming processes, the transfer member immediately before entering the transfer position or the secondary transfer position from the primary transfer member to the secondary transfer member has a polarity opposite to that of the toner due to friction or the like. When charged, a phenomenon called so-called pre-transfer may occur in which the toner on the latent image carrier is electrostatically attracted and adhered by the charge. When such pre-transfer occurs, the position at which the toner adheres to the transfer body deviates from the original position,
The image is easily disturbed.

Therefore, various methods and apparatuses for reducing the pre-transfer caused by the electric charge of the transfer body have been proposed. For example, JP-A-7-3192
No. 99, the lower guide plate for guiding the transfer sheet to the transfer position while supporting it from below is grounded, and the end of the lower guide plate is positively brought into contact with the back surface of the paper. An image forming apparatus configured as described above is described. According to this image forming apparatus, before the paper is conveyed to the transfer position, the electric charge of the paper can be removed from the lower guide plate, which comes into contact with the back surface of the paper, by grounding.

[0005]

However, in the image forming apparatus disclosed in JP-A-7-319299, the upper guide plate supporting the paper on the front surface and the front surface are positively brought into contact with each other. It is not a simple configuration. For this reason,
Even if the upper guide plate and the lower guide plate are grounded, the electric charge existing on the transfer surface, which is the front surface of the paper, cannot be reliably removed. Therefore, there is a possibility that pre-transfer may occur due to the influence of the charge existing on the transfer surface of the sheet.

The present invention has been made in view of the above background, and an object of the present invention is to provide an image forming apparatus capable of eliminating pre-transfer caused by electric charges existing on a transfer surface of a transfer body. That is.

[0007]

In order to achieve the above object, the invention of claim 1 provides a visible image holding member for holding a visible image made of a charged developer, and a method for transferring the visible image to the visible image holder. A transfer unit that transfers the transfer body to the transfer body at a transfer position that is a position facing the visual image holding body; and a conveyance unit that conveys the transfer body to the transfer position. The transfer unit transfers the visible image to the transfer body. In an image forming apparatus for forming an image, an AC power supply for generating an AC voltage,
An electrode connected to the AC power source and disposed at a position upstream of the transfer position in the transport direction of the transfer body toward a charge on a transfer surface of the transfer body so as to generate a discharge. It is characterized by having.

[0008] In this image forming apparatus, the transfer surface of the transfer body, which is about to be moved to the transfer position by the transport means, can be subjected to AC discharge by discharging from the electrodes.

According to a second aspect of the present invention, there is provided a latent image carrier capable of carrying a latent image and exhibiting a function as the visible image carrier.
2. The image forming apparatus according to claim 1, further comprising: a developing device that attaches a developer to the latent image to develop the latent image. It is a position where a visual image is transferred.

In this image forming apparatus, the transfer surface of the transfer body which is about to enter the transfer position, which is the position facing the latent image carrier, is subjected to AC static elimination.

According to a third aspect of the present invention, there is provided a latent image carrier for carrying a latent image, a developing device for attaching a developer to the latent image to develop the latent image, and a developing device for developing the latent image on the latent image carrier. A primary transfer member as the visible image holding member for primary transfer of the visible image,
And a secondary transfer member for secondary-transferring the visible image on the primary transfer member. The image forming apparatus according to claim 1, wherein the transfer position is from the primary transfer member to the secondary transfer member. This is a secondary transfer position where the transfer of the visible image is performed.

In this image forming apparatus, the transfer surface of a secondary transfer body such as a sheet which is about to enter a secondary transfer position where the secondary transfer is performed is subjected to AC static elimination.

4. The developing device according to claim 2, further comprising a developing device having a developer carrier for carrying a developer, and a developing power supply for applying a developing voltage to the developer carrier to form a developing electric field. In the above image forming apparatus, the developing electric field is formed by applying a voltage containing at least an AC component as the developing voltage.

In this image forming apparatus, a developing power source for applying a developing voltage containing at least an AC component can be shared as an AC power source for the electrodes.

According to a fifth aspect of the present invention, there is provided a visible image holding member for holding a visible image made of a charged developer, and a transfer position for transferring the visible image to the visible image holding member. A transfer unit that transfers the transfer body to the transfer body, and a transfer unit that transfers the transfer body to the transfer position, wherein the image forming apparatus transfers the visible image to the transfer body to form an image. Also, a transfer member charging means for charging the transfer surface of the transfer member to the same polarity as the charging polarity of the developer is provided on the upstream side in the transport direction of the transfer member.

In the pre-transfer caused by the electric charge on the transfer surface of the transfer member, the electric charge having the opposite polarity to the charge polarity of the developer causes the developer on the visible image holding member to be electrostatically directed toward the transfer surface. It is caused by the attraction. Therefore, in this image forming apparatus, the transfer surface of the transfer body that is about to enter the transfer position by the transport unit is charged to the same polarity as the developer by the transfer body charging unit. In such an image forming apparatus, even if the charge of the opposite polarity exists on the transfer surface on the upstream side of the transfer position in the transport direction of the transfer body, the charge is neutralized by the transfer body charging unit. Further, after the neutralization is performed in this manner, a charge having the same polarity as the charge polarity is generated on the transfer surface, and the charge and the developer on the visible image holding member are electrostatically repelled. By repelling in this manner, even if the charge of the opposite polarity exists on the back surface of the transfer member, the electrostatic attraction between the charge and the developer on the visible image holding member can be reduced.

According to a sixth aspect of the present invention, there is provided a latent image carrier capable of carrying a latent image and exhibiting a function as the visible image carrier.
6. The image forming apparatus according to claim 5, further comprising: a developing device that attaches a developer to the latent image to develop the latent image. It is a position where a visual image is transferred.

In this image forming apparatus, the charge present on the transfer surface of the transfer body which is about to enter the transfer position, which is the position facing the latent image carrier, is neutralized.
Further, the electrostatic attraction between the charge existing on the back surface of the transfer member and the developer on the visible image holding member is reduced. This eliminates pre-transfer caused by charges of a polarity opposite to that of the developer present on the transfer surface for transferring a visible image on the latent image carrier, and The pre-transfer caused by the electric charge existing in the image can be reduced.

According to a seventh aspect of the present invention, there is provided a latent image carrier for carrying a latent image, a developing device for attaching a developer to the latent image to develop the latent image, and a developing device for developing the latent image on the latent image carrier. A primary transfer member as the visible image holding member for primary transfer of the visible image,
6. The image forming apparatus according to claim 5, further comprising: a secondary transfer body as the transfer body that secondarily transfers the visible image on the primary transfer body. 5. This is a secondary transfer position at which the visible image is transferred to the next transfer member.

In this image forming apparatus, the charge present on the transfer surface of the secondary transfer member which is about to enter the secondary transfer position is neutralized, and the charge present on the back surface of the secondary transfer member is further neutralized. And the developer on the primary transfer member to reduce electrostatic attraction. Thus, the pre-transfer caused by the charge of the opposite polarity to the developer existing on the transfer surface of the secondary transfer body is eliminated, and the pre-transfer caused by the electric charge present on the back surface is reduced. be able to.

According to an eighth aspect of the present invention, in the image forming apparatus of the fifth, sixth or seventh aspect, the transfer body charging means is provided with a means for applying an AC / DC superimposed voltage to the transfer body. Is what you do.

The charging method of the transfer member charging means of the image forming apparatus according to the present invention includes a so-called brush rubbing method in which a charging brush is rubbed on the transfer member, and a so-called pulsating flow in which an AC / DC superimposed voltage is applied to the transfer member. A voltage application method or the like can be considered. However, in the case of the brush rubbing method, it is necessary to secure a space for disposing the charging brush near the transfer position, and this space may increase the size of the apparatus. Therefore, in the image forming apparatus according to the present invention, a pulsating voltage applying method of applying an AC / DC superimposed voltage to the transfer body is provided as the transfer body charging means. In such a transfer member charging unit, a space for disposing a flat electrode having a smaller thickness than the charging brush may be secured near the transfer position. Secured space is reduced.

According to a ninth aspect of the present invention, there is provided the developing device having a developer carrier for carrying a developer, and a developing power supply for applying a developing voltage to the developer carrier to form a developing electric field. 9. The image forming apparatus according to claim 8, wherein an AC / DC superimposed voltage is applied as the developing voltage to form the developing electric field.

In this image forming apparatus, the power supply for development can be shared as the power supply for the transfer member charging means.

According to a tenth aspect of the present invention, in the image forming apparatus of the ninth aspect, the developing voltage from the developing power source is supplied to the transfer member charging means via a resistor. Is what you do.

In this image forming apparatus, the value of the DC component of the AC / DC superimposed voltage applied to the transfer member is obtained by supplying the developing voltage from the developing power source to the transfer member charging means via the resistor. Is lower than the value of the DC component of the developing voltage. The transfer body to which the AC / DC superimposed voltage with the reduced DC component value is applied has a lower charging potential than when the developing voltage is directly applied.

According to an eleventh aspect of the present invention, in the image forming apparatus of the ninth aspect, the developing voltage from the developing power source is supplied to the transfer body charging means via a resistor and a capacitor connected in parallel to the resistor. It is characterized in that it is supplied.

In this image forming apparatus, the DC component of the developing voltage from the developing power supply cannot pass through the capacitor, but is supplied to the transfer member charging means via a resistor connected in parallel with the capacitor. You. On the other hand, the AC component of the developing voltage from the developing power supply is supplied to the transfer body charging means through a capacitor having a smaller load than the above-mentioned resistor, if the capacitor has a capacitance corresponding to the frequency. In such a configuration, even if the condition that the AC component of the developing voltage is not less than twice the charging start potential of the DC component is not satisfied, only the DC component can be reduced to satisfy this condition. become able to. It is known that when such conditions are satisfied, the charging potential of the transfer member can be stabilized.

According to a twelfth aspect of the present invention, there is provided a pressing roller for pressing the transfer member at the transfer position while sandwiching the transfer member between the transfer member and the visible image holding member, and the pressing roller has a polarity opposite to the charging polarity of the developer. The transfer means having a transfer voltage applying means for applying a transfer voltage, and the visible image holding member having an arcuate surface facing the pressing roller at the transfer position,
5. The method according to claim 5, wherein a sheet is used as the transfer body.
The image forming apparatus according to any one of 9, 10 and 11, wherein the conveying means is configured to enter the transfer position while bringing the sheet into contact with the arcuate surface.

As in this image forming apparatus, a transfer voltage having a polarity opposite to the charging polarity of the developer is applied to the pressing roller, and the transfer is performed between the pressing roller and the arcuate surface of the visible image holding member. When a sheet of paper is sandwiched, the charge of the opposite polarity may be injected into the roller contact portion of the sheet.
This charge of the opposite polarity electrostatically attracts the developer on the visible image holding member, but does not cause pre-transfer as long as it is injected into the roller contact portion at the transfer position. Even if charge is injected into the roller contact area,
This is because the developer on the visible image holding member is transferred onto the paper at the regular transfer position. However, a charge of the same polarity as the above-mentioned charge polarity is given to the transfer surface of the sheet immediately before entering the transfer position by the transfer body charging means, and this charge and the charge on the surface of the pressing roller are attracted to each other. Appropriate electrostatic force acts. Then, depending on the magnitude of the electrostatic force, the sheet immediately before entering the transfer position is bent toward the pressing roller, and the bending causes the sheet to contact the pressing roller. As described above, when the paper and the pressing roller come into contact with each other, the charges of the opposite polarity are injected into the paper not at the transfer position but at the upstream side of the transfer position in the paper transport direction, and the cause of the pre-transfer is caused. There is a possibility that. Therefore, in this image forming apparatus, the sheet is caused to enter the transfer position while making contact with the arcuate surface of the visible image holding member. When the sheet advances to the transfer position in this manner, the separation distance between the sheet and the pressing roller is increased in a region where the visible image holding member and the pressing roller are located on the upstream side in the sheet conveying direction from the transferring position. The maximum length can be secured. By ensuring such a long separation distance, the electrostatic force acting on the sheet can be reduced more than in the case where the sheet immediately before entering the transfer position is not brought into contact with the visible image holding member. Reduce. Then, by reducing the electrostatic force in this way, it is possible to reduce the contact between the sheet and the pressing roller due to the electrostatic force.

According to a thirteenth aspect of the present invention, there is provided the image forming apparatus of the fifth, sixth, seventh, eighth, ninth, tenth, eleventh or twelfth aspect, further comprising a guide member for guiding the transfer member to the transfer position while supporting the transfer member. The guide member is made of a conductive material and grounded.

In the image forming apparatus having the transfer member charging means and the guide member, the transfer member charged to the same polarity as the developer is charged by the transfer member charging means. When the guide member rubs against the guide member, the guide member may have a charge having a polarity opposite to the charge polarity due to frictional charging. When the guide member has such a charge, the floating developer floating in the apparatus and the developer on the visible image holding member are electrostatically attracted to the charge and adhere to the surface of the guide member. . The adhered developer may be transferred from the guide member to the back surface of the transfer member when the transfer member slides on the guide member, thereby causing back transfer of the transfer member. Therefore, in this image forming apparatus, the charge generated on the guide member due to the rubbing with the transfer member is released to the ground so that the guide member is not charged. In this manner, if the charging of the guide member is avoided, it is possible to prevent the developer from adhering to the guide member due to the charge.

According to a fourteenth aspect of the present invention, there is provided a pressing member which presses the transfer member at the transfer position while sandwiching the transfer member between the transfer member and the visible image holding member, and a transfer voltage application for applying a transfer voltage to the pressing member. And a guide member for guiding the transfer member to the transfer position while supporting the transfer member, and transferring between the pressing member and the visible image holding member by applying the transfer voltage. 7. An electric field is formed.
In the image forming apparatus of 7, 8, 9, 10, 11 or 12, the guide member made of a conductive material is grounded via a resistor, or the guide member is made of a medium resistance material and grounded. It is characterized by doing.

In general, paper as a transfer body is insulative, but when it is placed in a high-temperature and high-humidity environment, it may become conductive due to moisture absorption or the like. In a device in which the guide member is grounded as in this image forming apparatus, when the transfer body becomes conductive in this way, a current caused by a transfer voltage causes the transfer member and the guide member to move from the pressing member to the transfer member. May leak to ground via When the current leaks in this manner, the intensity of the transfer electric field is reduced, and transfer failure occurs. Therefore, in this image forming apparatus, the guide member made of a conductive material is grounded via a resistor, or the guide member is made of a medium-resistance material and grounded, so that It makes it difficult for current to leak to the ground.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic printer (hereinafter, referred to as a printer) as an image forming apparatus will be described below. First, a basic configuration of the printer according to the present embodiment will be described. FIG. 1 is a configuration diagram schematically showing a main part of the printer. FIG. 2 is a configuration diagram showing a main configuration of an image forming unit of the printer. In each of these drawings, the image forming unit 1 includes a latent image forming unit 2 and a developing unit 3.

The latent image forming section 2 is provided with a photosensitive drum 4 as a latent image carrier, a charging roller 5, a cleaning blade 6, and the like. The photoreceptor drum 4 is rotated in a counterclockwise direction in the figure by a driving unit (not shown), and has a uniform surface of positive or negative polarity by rubbing with the charging roller 2 rotated in a clockwise direction in the figure. Is charged. As described above, the method of charging the photosensitive drum using the charging roller 2 has an advantage that the amount of generated ozone can be greatly reduced as compared with the charging method using the corotron method. An electrostatic latent image is formed on the surface of the photosensitive drum 1 charged by rubbing with the charging roller 2 by a writing unit such as an exposure device (not shown). The electrostatic latent image is conveyed to a position facing the developing unit 3 as the photosensitive drum 1 rotates.

The developing section 3 includes a toner T as a developer.
, Agitators 8 and 9 provided in the toner storage unit 7, a toner storage unit 10 for storing the toner T discharged from the toner storage unit 7, and a toner storage unit 10 in the toner storage unit 10. Stirring member 1 for stirring toner T
1, a developing roller 12 as a developer carrier, a thinning blade 13, a developing bias power supply 14, and the like. The agitators 8 and 9 are respectively driven to rotate counterclockwise in the figure by driving means (not shown), and discharge the toner T in the toner storage unit 7 toward the toner accumulation unit 10 while stirring. The toner T discharged in this way stays in the toner staying section 10 while being stirred by the stirring member 11 which is driven to rotate counterclockwise in FIG. This agitation promotes frictional charging of the toner T in the toner stagnation section 10. On the right side of the toner accumulating portion 10 in the drawing, the developing roller 12 that is driven to rotate clockwise in the drawing by driving means (not shown) is disposed, and carries the toner T in the toner accumulating portion 10. . As the carried toner T passes the contact position between the developing roller 12 and the thinning blade 13 with the rotation of the developing roller 12, the layer thickness is regulated and the toner becomes a thin toner layer. ,
Tribocharging is further promoted. The developing roller 12 partially exposes from an opening provided in the developing unit 3 to maintain a small gap between the exposed portion and the photosensitive drum 1. A developing bias, which is an AC / DC superimposed voltage, is applied from the developing bias power supply 14 as a developing power supply, whereby a developing electric field is formed in the minute gap. The thin toner layer on the developing roller 12 is affected by the electrostatic force of the developing electric field when passing through the minute gap, and causes toner to adhere to the electrostatic latent image on the photosensitive drum 1, The electrostatic latent image is developed into a toner image. The developing unit 3 for developing an electrostatic latent image as described above uses a so-called non-contact developing method in which the thin toner layer is not directly in contact with the photosensitive drum 1, and an AC / DC developing bias is used as the developing bias. By applying a superimposed voltage, the toner T in the minute gap is reciprocated between the developing roller 12 and the photosensitive drum 1. The developing bias has, for example, a peak-to-peak (Vp-p) value obtained by superimposing a DC bias of -300 to -600 [V] on an AC bias.
Frequency 0.8 to 2.5 [kHz] at 5-2.2 [kV]
Pulse voltage.

On the right side of the image forming unit 1 in the figure, a transfer roller 15 as a pressing roller and a transfer unit including a transfer bias power supply (not shown) as a transfer voltage applying unit are provided. This transfer means is provided by the transfer roller 1
5 is brought into contact with the photosensitive drum 1 to form a transfer nip as a transfer position, and a transfer electric field is formed in the transfer nip by applying a transfer bias having a polarity opposite to that of the toner T.

At the lower part of the printer main body, there is provided a paper feed cassette 16 for accommodating a transfer paper bundle in which a plurality of transfer papers 50 which are transfer bodies and paper are stacked. The paper feed roller 17 is in contact with the transfer paper 50. When the paper feed roller 17 is driven to rotate counterclockwise in the figure by a driving unit (not shown), the transfer paper 50 is supplied from inside the paper feed cassette 16 toward between the rollers of the registration roller pair 18. ing.

The registration roller pair 18 is rotated by a driving means (not shown) at a timing when the toner image and the transfer paper 50 can be overlapped at the transfer nip, and sends the transfer paper 50 to the transfer nip. .

A guide mechanism for guiding the transfer paper 50 sent from the pair of registration rollers 18 to the transfer nip is provided upstream of the transfer nip in the transfer paper transport direction. Specifically, the guide mechanism is a part of the casing of the image forming unit 1, and includes a transfer surface guide portion 1a that guides the transfer paper 50 to the transfer nip while supporting the transfer paper 50 on the transfer surface side; 1a, and a back guide member 22 for guiding the transfer paper 50 to the transfer nip while supporting the transfer paper 50 on the back.

The toner image on the photosensitive drum 1 developed by the developing unit 3 is transferred to the transfer nip at the transfer nip.
The transfer paper 50 guided by such a guide mechanism
Under the influence of the pressing force of the transfer roller 15 and the electrostatic force of the transfer electric field, the image is transferred from the photosensitive drum 1 onto the transfer paper 50.

The transfer paper 5 on which the toner image has been transferred as described above.
No. 0 is conveyed between the heating roller 19a and the pressure roller 19 in the fixing device 19 through the transfer nip, and the toner image is fixed. Then, the discharge roller pair 20
Is discharged out of the machine through the rollers.

The residual toner remaining on the surface of the photosensitive drum 1 after passing through the transfer nip is mechanically scraped off from the surface by the cleaning blade.

In the above configuration, the transfer paper 50 before being conveyed to the transfer nip may be charged for various reasons to cause pre-transfer. For example, the transfer paper 50 may be frictionally charged by rubbing with other transfer paper in the paper feed cassette 16, the transfer surface guide 1a, the back surface guide member 22, and the like. Further, for example, since the transfer paper 50 printed on one side is injected with electric charge from the transfer roller 15 to the back side when passing through the transfer nip, the back side serving as the transfer surface at the time of printing the back side is charged. . Therefore, in the printer according to the present embodiment,
By providing the following characteristic configuration, pre-transfer caused by the charge of the transfer paper 50 is reduced.

Hereinafter, this characteristic configuration will be described. FIG. 3 is a configuration diagram showing a device around the photosensitive drum 1 of the printer. In FIG. 3, the transfer surface guide 1
A conductive mylar 21 as an electrode is disposed above the upper surface a so as to face the back guide member 22 and contact the transfer paper 50 sent from the registration roller pair 18. The developing bias power supply 14 is connected to 21. The developing bias power supply 14 and the conductive mylar 21 function as charging means for charging the transfer surface of the transfer paper 50. Specifically, when the conductive mylar 21 connected to the developing bias power source 14 comes into contact with the transfer surface of the transfer paper 50 sent from the registration roller pair 21, the conductive mylar 21 contacts the contact portion with an alternating current.
The contact portion is charged by applying a DC superimposed voltage.

The charged potential value of the transfer surface of the transfer paper 50 depends on the ratio between the AC component and the DC component of the developing bias, the value of the DC component, and the like, but is at most approximately equal to the value of the DC component. Become. In this printer, a negatively-charged toner T is used, and a negative-polarity voltage is applied as the DC component. The transfer surface of the transfer paper 50 in contact with the conductive mylar 21 is It will be negatively charged with the same polarity.

In this printer for charging the transfer paper 50 in this way, even if the transfer surface of the transfer paper 50 immediately before entering the transfer nip has a positive charge due to single-sided printing or the like, the transfer surface is negative. The charge is neutralized by being charged. Further, a negative charge is applied to the transfer surface, and electrostatically repels the toner T having a negative charge on the photosensitive drum 1. Thus, even if the back surface of the transfer paper 50 has a positive charge due to single-sided printing or the like, the electrostatic attraction between the charge and the toner T on the photosensitive drum 1 is reduced. Is done.

As described above, according to the printer of the present embodiment, even if a positive charge causing pre-transfer exists on the transfer surface of the transfer paper 50, the charge is neutralized. Transfer can be eliminated. Furthermore,
Even if a positive charge that causes pre-transfer exists on the back surface of the transfer paper 50, the electrostatic attraction between the charge and the toner T on the photosensitive drum 1 is reduced, so that the pre-charge generated by the charge is reduced. Transfer can be reduced.

The negative charge given to the transfer surface of the transfer paper 50 by the conductive mylar 21 or the like is transferred to the toner T on the photosensitive drum 1 at the transfer nip.
To the transfer paper 50. However, in this printer, even if such an electrostatic force acts, the photosensitive drum 1
The value of the transfer bias is adjusted so as to form the transfer electric field having a strength enough to transfer the toner T to the transfer paper 50, and the electrostatic force does not cause transfer failure.

In this embodiment, the transfer paper 50
Although the printer in which the transfer surface is charged to a polarity opposite to that of the toner T by applying an AC / DC superimposed bias to the transfer surface described above has been described, the charging means in the present invention is not limited to this. For example, a charging brush, a charging charger, or the like may be used as the charging unit. However, in the present printer, as shown in FIG. 3, it is not necessary to secure a space for disposing the charging brush and the charging charger upstream of the transfer nip, and the size of the apparatus body is increased by securing the space. Has been avoided. Further, the developing bias power supply 14 is used as a power supply for applying an AC / DC superimposed bias to the conductive mylar 21, thereby avoiding an increase in cost due to the provision of a dedicated power supply for applying the AC / DC superimposed bias. I have.

Next, a printer according to an embodiment in which a more characteristic configuration is added to the printer according to this embodiment will be described. [Example 1] Transfer paper 5 immediately before entering the transfer nip
Since a negative charge is applied to the transfer surface 0 by the conductive mylar 21 or the like, the transfer roller 15 and the transfer paper 50, which have a polarity opposite to that of the toner T by applying the transfer bias, that is, have a positive charge. And an electrostatic force acting on each other acts. Transfer paper 50 with excellent flexibility
In such a case, the electrostatic force acts just before entering the transfer nip, so that the contact may be made to wind around the transfer roller 15 and a positive charge may be injected into the back surface. is there. Therefore, in the printer of the first embodiment, as shown in FIG. 4, the tip of the back guide member 22 is made to project toward the photosensitive drum 1 beyond a virtual extension line L1 extending straight from the transfer nip. Thus, the transfer paper 50 is caused to enter the transfer nip while being in contact with the photosensitive drum 1. When the transfer paper 50 is made to enter in this way, the transfer paper 5 is located in an area P between the photosensitive drum 1 and the transfer roller 15 upstream of the transfer nip in the transfer paper transport direction.
0 and the transfer roller 15 can be kept as long as possible. Thus, the electrostatic force acting on the transfer paper 50 immediately before entering the transfer nip can be reduced, and pre-transfer caused by the electrostatic force can be reduced.

[Embodiment 2] FIG. 5 is a schematic diagram showing the back guide member 22 of the printer according to the second embodiment. In FIG. 5, the back surface guide member 22 is made of a conductive material and is in an electrically grounded state. In such a back surface guide member 22, the charge generated by the rubbing with the transfer paper 50 is released to the ground, so that the frictional charging due to the rubbing can be avoided. As a result, it is possible to avoid adhesion of the toner due to charging, and to avoid back stain of the transfer paper 50 due to the adhesion of the toner.

However, if the conductive back guide member 22 is grounded and the transfer paper 50 becomes conductive due to moisture absorption or the like, the current caused by the transfer bias is transferred from the transfer roller 15 to the transfer paper 50 and the back guide. There is a case where the intensity of the transfer electric field is reduced by leaking to the ground via the member 22. This may cause transfer failure. Therefore, when there is a high possibility that the transfer bias leaks to the ground due to moisture absorption of the transfer paper 50 or the like, the back guide member 22 is made of a medium-resistance material, or as shown in FIG. It is desirable to ground the back surface guide member 22 via R. By doing so, it is difficult for the current from the transfer roller 15 to leak to the ground, and transfer defects due to the leak can be reduced.

The material having the medium resistance is 10 ⁶
It is preferable to use one having a resistivity of 10 to ^{12 12} [Ωcm].

[Embodiment 3] As described above, the charging potential value of the transfer surface of the transfer paper 50 is at most the same value as the DC component of the developing bias. It is adjusted by the developing conditions such as the linear velocity of the body drum 1 and the developing roller 12, the uniform charging potential of the photosensitive drum 1, the charging characteristics of the toner T, and the particle shape. If the transfer surface is charged to a value equivalent to the DC component adjusted in this manner, the transfer electric field may be disturbed and transfer failure may occur. Therefore, in the printer of the third embodiment, FIG.
As shown in (1), the developing bias from the developing bias power supply 14 is supplied to the conductive mylar 21 via a resistor R. As shown in the graph of FIG. 8, the voltage supplied to the conductive mylar 21 (hereinafter referred to as charging bias) in this manner has a Vp-p value and a DC component value (t from the center of Vp-p). (Deviation from the axis) is smaller than that of the developing bias. Then, the charged potential value of the transfer surface of the transfer paper 50 is reduced by reducing the value of the DC component. For this reason, the transfer surface can be charged to an appropriate value by avoiding excessive charging of the transfer surface caused when the developing bias is applied to the transfer surface at the same value.

Conventionally, the Vp-p value of the charging bias used for charging has a charging start potential (600
It is known that the charge potential of the member to be charged can be stabilized irrespective of environmental fluctuations when the value is twice or more (around V). Therefore, when the Vp-p value is less than twice the charging start potential of the DC component, as shown in FIG.
It is desirable to supply the conductive mylar 21 to the conductive mylar 21 via a capacitor C connected in parallel with the conductive mylar 21. By doing so, as shown in FIG. 10, only the value of the DC component of the charging bias is reduced, and Vp-p value>
This is because the condition of DC component × 2 can be satisfied.

However, in the non-contact one-component developing system, a developing bias (AC · D) having a value that causes the toner to reciprocally fly between the developing roller and the photosensitive drum and does not generate electric discharge.
C superimposed bias) is applied. With such a developing bias, the Vp-p value of the AC component generally tends to be twice or more the DC component. In the image forming apparatus according to the present invention, by using such a developing bias as a charging bias, the charging potential of the transfer sheet can be easily stabilized.

In the above embodiments and examples, the printer in which the transfer paper 50 as the transfer member is sandwiched between the transfer nips as the transfer position has been described. The present invention can also be applied to an image forming apparatus that conveys the image to a printer.

Further, the printer in which the transfer surface of the transfer paper 50 which is to enter the transfer nip is charged has been described. However, if the transfer surface is not desired to be charged for some reason, the transfer surface may be charged. AC static elimination may be performed. When the transfer surface is to be subjected to AC static elimination, as shown in FIG. 11, the developing bias from the developing bias power supply 14 is supplied to the conductive mylar 21 via a capacitor C, and the transfer paper 50 is subjected to AC. What is necessary is just to arrange | position the said conductive mylar 21 in the position which can be discharged. In this manner, a neutralization bias composed of an AC wave as shown in FIG. 12 is applied to the conductive mylar 21 so that the transfer surface of the transfer paper 50 passing through the position facing the conductive mylar 21 is applied. As a result, an AC discharge is generated from the conductive mylar 21, whereby the transfer surface can be discharged. Then, pre-transfer caused by the charge on the transfer surface can be eliminated by eliminating the charge on the transfer surface in this manner.

The printer which performs only the primary transfer from the photosensitive drum 4 to the transfer paper 50 has been described.
The secondary transfer of the image forming apparatus for performing the primary transfer from the photosensitive drum 4 to a primary transfer body such as an intermediate transfer belt and the secondary transfer from the primary transfer body to the transfer paper 50 is also described in the present invention. Applicable.

[0062]

According to the first aspect of the present invention, the transfer surface of the transfer body which is about to enter the transfer position by the transfer means can be subjected to AC static elimination. There is an excellent effect that transfer can be eliminated.

According to the second aspect of the present invention, the transfer surface of the transfer body which is about to enter the transfer position, which is the position facing the latent image carrier, is subjected to AC static elimination. There is an excellent effect that pre-transfer generated on the transfer body for transferring a visible image can be eliminated.

According to the third aspect of the present invention, since the transfer surface of the secondary transfer body which is about to enter the secondary transfer position is subjected to AC static elimination, it is possible to eliminate the pre-transfer generated on the secondary transfer body. There is an excellent effect that it can be done.

According to the fourth aspect of the present invention, since the developing power supply can be shared as the AC power supply for the electrodes, an excellent effect that the cost increase caused by providing the latter power supply can be avoided can be avoided. is there.

According to the fifth aspect of the present invention, even if "charge having a polarity opposite to that of the developer", which causes pre-transfer, exists on the transfer surface of the transfer member, the charge is transferred to the transfer member charging means. Therefore, there is an excellent effect that pre-transfer caused by electric charges existing on the transfer surface can be eliminated. Furthermore, even if the charge of the opposite polarity exists on the back surface of the transfer member, the electrostatic attraction between the charge and the developer on the visible image holding member can be reduced. There is an excellent effect that the pre-transfer caused by the generated charges can be reduced.

According to the sixth aspect of the present invention, the pre-transfer generated by the charge of the opposite polarity to the developer present on the transfer surface is transferred to the transfer member for transferring the visible image on the latent image carrier. There is an excellent effect that the pre-transfer caused by the electric charges existing on the back surface can be reduced and the pre-transfer caused by the electric charge existing on the back surface can be reduced.

According to the seventh aspect of the present invention, the pre-transfer generated on the secondary transfer member due to the charge of the opposite polarity to the developer present on the transfer surface is eliminated, and the charge existing on the back surface is used. The resulting pre-transfer can be reduced.

According to the eighth aspect of the present invention, the space to be secured near the transfer position is made smaller than in the case where a charging brush is provided as the transfer body charging means. There is an excellent effect that can be.

According to the ninth aspect of the present invention, the power supply for development can be shared as the power supply for the transfer member charging means.
There is an excellent effect that the cost increase caused by providing the latter power supply can be avoided.

According to the tenth aspect of the present invention, the charging potential of the transfer member is made lower than when the developing voltage is directly applied to the transfer member. Therefore, the transfer member generated when the developing voltage is applied as it is. This is an excellent effect that the transfer member can be charged to an appropriate value by avoiding excessive charging of the transfer member.

According to the eleventh aspect, even when the condition that the AC component of the developing voltage is not less than twice the charging start potential of the DC component is not satisfied, the charging potential of the transfer member can be stabilized. There is an excellent effect that it can be achieved.

According to the twelfth aspect of the present invention, the sheet and the pressing roller caused by the electrostatic force of the electric charge can be formed more than when the sheet immediately before entering the transfer position is not brought into contact with the visible image holding member. Therefore, there is an excellent effect that pre-transfer caused by charge injection from the pressing roller into the paper due to the contact can be reduced.

According to the thirteenth aspect of the present invention, it is possible to prevent the developer from adhering to the guide member due to the electric charge on the guide member. There is an excellent effect that it can be done.

According to the fourteenth aspect of the present invention, even if the transfer member becomes conductive due to moisture absorption or the like, the current that attempts to leak to the ground from the pressing member via the transfer member and the guide member is provided. Since it is difficult to leak, there is an excellent effect that transfer defects due to the leak can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing a main part of a printer according to an embodiment.

FIG. 2 is a configuration diagram showing a main configuration of an image forming unit of the printer.

FIG. 3 is a configuration diagram showing a device around a photosensitive drum of the printer.

FIG. 4 is a configuration diagram illustrating a device around a photosensitive drum of the printer according to the first embodiment.

FIG. 5 is a schematic diagram illustrating a back guide member of the printer according to the second embodiment.

FIG. 6 is a schematic view showing a modified example of the grounding method for the back guide member.

FIG. 7 is a schematic diagram illustrating a connection state of a developing bias power supply of the printer according to the third embodiment.

FIG. 8 is a graph showing waveforms of a developing bias and a charging bias of the printer.

FIG. 9 is a schematic diagram showing a modification of the connection state.

FIG. 10 is a graph showing waveforms of a developing bias and a charging bias in a modified example of the connection state.

FIG. 11 is a schematic diagram showing the same connection state of a modified apparatus in which a transfer surface of a transfer paper is removed.

FIG. 12 is a graph showing waveforms of a developing bias and a discharging bias in the device of the modified example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming unit 2 Latent image forming part 3 Developing part 4 Photoreceptor drum 5 Charging roller 6 Cleaning blade 7 Toner storage part 8, 9 Agitator 10 Toner retention part 11 Stirring member 12 Developing roller 13 Thinning blade 14 Development bias power supply 15 Transfer roller 16 Paper feed cassette 17 Paper feed roller 18 Registration roller pair 19 Fixing device 20 Paper discharge roller pair 21 Conductive mylar 22 Back guide member 50 Transfer paper

Claims (14)

[Claims] 1. A visible image holding member for holding a visible image comprising a charged developer, and a transfer for transferring the visible image to a transfer member at a transfer position opposite to the visible image holding member. Means for transferring the visible image to the transfer body to form an image, comprising: an AC power supply for generating an AC voltage; An electrode that is connected to an AC power supply and that is disposed at a position on the upstream side in the transport direction of the transfer body from the transfer position where discharge can be generated toward charges on the transfer surface of the transfer body. An image forming apparatus comprising: A latent image carrier capable of carrying a latent image and exhibiting a function as the visible image carrier; and a developing device for attaching a developer to the latent image to develop the latent image. Claim 1 comprising
The image forming apparatus according to claim 1, wherein the transfer position is a position where the visible image is transferred from the latent image carrier to the transfer body. 3. A latent image carrier for carrying a latent image, a developing device for attaching a developer to the latent image to develop the latent image, and the visible image developed on the latent image carrier. The image forming apparatus according to claim 1, further comprising a primary transfer member as the visible image holding member for primary transfer, and a secondary transfer member for secondary transfer of the visible image on the primary transfer member. The image forming apparatus according to claim 1, wherein the transfer position is a secondary transfer position at which the visible image is transferred from the primary transfer member to the secondary transfer member. 4. A developing device having a developer carrying member for carrying a developer, and a developing power supply for applying a developing voltage to the developer carrying member to form a developing electric field. Or the image forming apparatus according to 3, wherein a voltage including at least an AC component is applied as the developing voltage to form the developing electric field. 5. A visible image holding member for holding a visible image made of a charged developer, and the visible image is transferred to the transfer member at a transfer position which is a position facing the visible image holding member. An image forming apparatus that includes a transfer unit and a transfer unit that transfers the transfer body to the transfer position, and transfers the visible image to the transfer body to form an image. An image forming apparatus comprising: a transfer body charging unit that charges a transfer surface of the transfer body on the upstream side in a transport direction to have the same polarity as a charge polarity of a developer. 6. A latent image carrier capable of carrying a latent image and exhibiting a function as the visible image carrier, and a developing device for attaching a developer to the latent image to develop the latent image. Claim 5 comprising
The image forming apparatus according to claim 1, wherein the transfer position is a position where the visible image is transferred from the latent image carrier to the transfer body. 7. A latent image carrier for carrying a latent image, a developing device for applying a developer to the latent image to develop the latent image, and the visible image developed on the latent image carrier 6. The image forming apparatus according to claim 5, further comprising: a primary transfer member serving as the visible image holding member that primarily transfers the image; and a secondary transfer member serving as the transfer member that secondarily transfers the visible image on the primary transfer member. An image forming apparatus, wherein the transfer position is a secondary transfer position where the transfer of the visible image from the primary transfer member to the secondary transfer member is performed. 8. An image forming apparatus according to claim 5, wherein said transfer member charging means includes means for applying an AC / DC superimposed voltage to said transfer member. 9. A developing device having a developer carrier for carrying a developer, and a developing power source for applying a developing voltage to the developer carrier to form a developing electric field. In the image forming apparatus of
An image forming apparatus, wherein a DC superimposed voltage is applied to form the developing electric field. 10. An image forming apparatus according to claim 9, wherein said developing voltage from said developing power source is supplied to said transfer member charging means via a resistor. 11. An image forming apparatus according to claim 9, wherein said developing voltage from said developing power supply is supplied to said transfer member charging means via a resistor and a capacitor connected in parallel with said resistor. An image forming apparatus comprising: 12. A pressing roller for pressing the transfer member at the transfer position while sandwiching the transfer member between the transfer member and the visible image holding member;
The transfer unit having a transfer voltage application unit that applies a transfer voltage having a polarity opposite to the charging polarity of the developer to the pressing roller; and an arc-shaped surface facing the pressing roller at the transfer position. The image forming apparatus according to any one of claims 5, 6, 7, 8, 9, 10, and 11, further comprising a visible image holding member, wherein a sheet is used as the transfer member. An image forming apparatus, wherein the transport unit is configured to enter a transfer position. 13. The image forming apparatus according to claim 5, further comprising a guide member for guiding the transfer body to the transfer position while supporting the transfer body.
9. The image forming apparatus according to 9, 10, 11 or 12, wherein the guide member is formed of a conductive material and grounded. 14. A pressing member which presses the transfer body at the transfer position while sandwiching the transfer body between the transfer member and the visible image holding member, and a transfer voltage applying means for applying a transfer voltage to the pressing member. A transfer member, and a guide member for guiding the transfer member to the transfer position while supporting the transfer member, wherein a transfer electric field is formed between the pressing member and the visible image holding member by applying the transfer voltage. Terms 5, 6, 7, 8, 9, 10,
In the image forming apparatus according to the eleventh or the twelfth aspect, the guide member made of a conductive material is grounded via a resistor, or the guide member is made of a medium-resistance material and grounded. Image forming device.